Chemistry — Chapter Practice, Grade 8

Use evidence and models to explain chemical change, conserve atoms, and track energy transfer.

Problem 1

Which of these is NOT necessarily a sign of a chemical reaction?
  1. Formation of a precipitate
  2. Gas bubbles forming
  3. A change of shape
  4. A color change
Answer and explanation

A change of shape

A change of shape alone (like bending or cutting) is a physical change, not evidence of a chemical reaction.

Problem 2

Mixing two clear solutions produces a cloudy solid that settles to the bottom. This solid is called a…
  1. reactant
  2. catalyst
  3. precipitate
  4. solvent
Answer and explanation

precipitate

A solid that forms and settles out of a solution during a reaction is called a precipitate.

Problem 3

A reaction releases energy, raising the temperature of a solution from 20°C to 35°C. What is the temperature change (ΔT)?
Answer and explanation

15 °C

ΔT = 35 − 20 = 15°C.

Problem 4

Name two signs that suggest a chemical reaction has occurred, and explain why each suggests a new substance formed.
Answer and explanation

Gas bubbles suggest a new gaseous substance is escaping that wasn't there before, and a color change suggests new compounds have formed with different light-absorbing properties than the original substances.

Problem 5

Which of these is an example of a chemical reaction?
  1. ice melting
  2. iron rusting
  3. water boiling
  4. sugar dissolving in tea
Answer and explanation

iron rusting

Rusting forms a new substance, iron oxide, so it is a chemical reaction — unlike the other physical changes listed.

Problem 6

Why isn't a temperature change alone considered definite proof of a chemical reaction?
Answer and explanation

Physical processes can also change temperature — for example, dissolving some substances absorbs or releases heat even though no new substance forms — so a temperature change is only a clue, not final proof.

Problem 7

A clear liquid forms bubbles when warmed. Give two possible explanations and one useful follow-up observation. Explain the reasoning in your own words.
Answer and explanation

Both physical gas release and chemical gas production are possible; bubbles alone are insufficient evidence.

One possibility is boiling or dissolved gas leaving the liquid.

Another possibility is a reaction producing gas; checking whether new substances formed helps distinguish them.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

Water bubbles when boiling. Explain why bubbles alone do not prove a reaction. Show the reasoning, not just the conclusion.
Hints

Use more than one observation and distinguish a precipitate from material present initially.

Answer and explanation

Water vapor forms during a physical phase change. Gas bubbles can arise without producing a new chemical substance.

Problem 9

A student reports only that a mixture became warm. Suggest a comparison that would strengthen a reaction claim.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Record temperatures and compare with separate mixing controls, then look for evidence of new composition. Warming alone can also accompany physical mixing or dissolving.

Problem 10

Compare supplied descriptions of cutting iron, forming rust and mixing an alloy. Give an appropriate mechanism and explain why “all chemicals are dangerous” and “every mixture is a new compound” fail.
Hints

Use the illustrated study titled Chemical interactions in daily life and history. Keep the observations, model and conditions separate.

Answer and explanation

Cutting can retain iron identity while rust formation produces different substances. An alloy can be a mixture rather than one fixed-ratio compound. Chemical risk cannot be decided from the word alone; identity, amount, exposure and use need evidence. Relate the chosen process to a practical effect while keeping ordinary atom rearrangement distinct from nuclear element formation.

Cutting can retain iron identity while rust formation produces different substances. An alloy can be a mixture rather than one fixed-ratio compound. Chemical risk cannot be decided from the word alone; identity, amount, exposure and use need evidence. Relate the chosen process to a practical effect while keeping ordinary atom rearrangement distinct from nuclear element formation.

Response criteria

  • Distinguish composition from appearance.
  • Explain a daily/historical consequence with a mechanism.
  • Evaluate blanket chemical/mixture claims with conditions.

Problem 11

New substances form when the same atoms regroupNew substances form when the same atoms regroupReactants: 2H₂ + O₂Products: 2H₂OBefore and after: 4 H atoms and 2 O atoms. New combinations form.Blue = H; red = O. Counting model only; no hydrogen ignition activity.
This supplied water-forming reaction contains four hydrogen atoms and two oxygen atoms on each side. Their combinations change from H₂ and O₂ to H₂O. Colored circles distinguish atom types rather than literal colors, and the bonds are counting aids. It is a different example from a bath-bomb reaction; the figure does not claim that a bath bomb contains hydrogen gas or oxygen gas.
For this unit’s illustrated case, what evidence in the diagram supports a chemical change without supporting creation of new atoms?
Answer and explanation

The product molecules have a different composition/combination from the reactant molecules, while each element’s atom count stays four H and two O.

A reactant is a starting substance and a product is a resulting substance. Different combinations can give different characteristic properties. The drawing is an explanation for an already specified reaction, not proof that every visible bubble is a new substance.

The product molecules have a different composition/combination from the reactant molecules, while each element’s atom count stays four H and two O.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 12

An unknown mixture forms bubbles, but a control shows trapped air can also form bubbles. What conclusion is justified now and what additional evidence should distinguish the explanations?
Answer and explanation

Bubbles are observed; a new chemical substance is not yet established. Obtain appropriate supplied gas-identity or characteristic-property evidence and compare the control/conditions.

Record appearance without assigning an unsupported identity.

Use a discriminating comparison rather than one visual sign.

Bubbles are observed; a new chemical substance is not yet established. Obtain appropriate supplied gas-identity or characteristic-property evidence and compare the control/conditions.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 13

12 g of carbon reacts with 32 g of oxygen to form carbon dioxide. What is the mass of carbon dioxide produced?
Answer and explanation

44 g

By conservation of mass: 12 g + 32 g = 44 g of carbon dioxide.

Problem 14

In a reaction, 25 g of reactant A combines with reactant B to form 60 g of product. What was the mass of reactant B?
Answer and explanation

35 g

60 g (products) − 25 g (reactant A) = 35 g of reactant B.

Problem 15

The law of conservation of mass says that in a chemical reaction…
  1. mass can be created but not destroyed
  2. the total mass of the reactants equals the total mass of the products
  3. products always weigh less than the reactants
  4. atoms are destroyed and new ones form
Answer and explanation

the total mass of the reactants equals the total mass of the products

Conservation of mass means reactant mass and product mass are always equal in a closed system.

Problem 16

Explain, in terms of atoms, why mass is conserved in a chemical reaction.
Answer and explanation

Atoms are only rearranged into new combinations (different molecules); no atoms are created or destroyed, so the total mass before and after the reaction stays the same.

Problem 17

5.0 g of magnesium burns in oxygen to form 8.3 g of magnesium oxide. How many grams of oxygen combined with the magnesium?
Answer and explanation

3.3 g

Oxygen used = 8.3 g (product) − 5.0 g (magnesium) = 3.3 g.

Problem 18

An open reaction starts with 80 g and leaves 77 g of material. If the only loss is gas, what mass escaped? Explain the reasoning in your own words.
Answer and explanation

3 g of gas; remaining material plus gas still totals 80 g.

Use initial mass=remaining mass+escaped mass.

Subtract 80−77=3 g.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 19

An open setup starts at 92 g and ends at 87 g. Assuming gas is the only loss, calculate escaped mass. Show the reasoning, not just the conclusion.
Hints

Count all products, including invisible gas.

Answer and explanation

92−87=5 g; remaining material plus escaped gas totals 92 g.

Problem 20

A sealed reaction reads 0.2 g less afterward. Name two checks before concluding mass conservation failed.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Check balance uncertainty and calibration, then leaks or spills and whether the same container parts were included. A measurement mismatch requires investigation.

Problem 21

New substances form when the same atoms regroupNew substances form when the same atoms regroupReactants: 2H₂ + O₂Products: 2H₂OBefore and after: 4 H atoms and 2 O atoms. New combinations form.Blue = H; red = O. Counting model only; no hydrogen ignition activity.
This supplied water-forming reaction contains four hydrogen atoms and two oxygen atoms on each side. Their combinations change from H₂ and O₂ to H₂O. Colored circles distinguish atom types rather than literal colors, and the bonds are counting aids. It is a different example from a bath-bomb reaction; the figure does not claim that a bath bomb contains hydrogen gas or oxygen gas.
For this unit’s illustrated case, what evidence in the diagram supports a chemical change without supporting creation of new atoms?
Answer and explanation

The product molecules have a different composition/combination from the reactant molecules, while each element’s atom count stays four H and two O.

A reactant is a starting substance and a product is a resulting substance. Different combinations can give different characteristic properties. The drawing is an explanation for an already specified reaction, not proof that every visible bubble is a new substance.

The product molecules have a different composition/combination from the reactant molecules, while each element’s atom count stays four H and two O.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 22

A specified product has mass 14 g after reacting with 9 g of the initial solid in an open apparatus. If incoming gas accounts for the change, how much gas mass must be included in a complete boundary?
Answer and explanation

5 g of incoming gas, so 9+5 = 14 g. The increase concerns matter crossing the measured boundary rather than matter being created.

Subtract the initial solid mass from product mass.

Identify the initially omitted matter source.

5 g of incoming gas, so 9+5 = 14 g. The increase concerns matter crossing the measured boundary rather than matter being created.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 23

In the balanced equation 2H₂ + O₂ → 2H₂O, how many total hydrogen atoms are on the reactant side?
  1. 2
  2. 4
  3. 6
  4. 8
Answer and explanation

4

2 molecules of H₂ each have 2 hydrogen atoms: 2 × 2 = 4 hydrogen atoms.

Problem 24

In the equation 2Mg + O₂ → 2MgO, how many oxygen atoms are on the product side?
Answer and explanation

2 atoms

2 MgO means 2 formula units, each with 1 oxygen atom, so there are 2 oxygen atoms total — matching the 2 oxygen atoms in O₂ on the reactant side.

Problem 25

Which coefficients correctly balance this equation? ___N₂ + ___H₂ → 2NH₃
  1. 1 and 1
  2. 1 and 3
  3. 2 and 3
  4. 1 and 2
Answer and explanation

1 and 3

N₂ + 3H₂ → 2NH₃ gives 2 N atoms and 6 H atoms on both sides.

Problem 26

Explain why you can change coefficients but not subscripts when balancing an equation.
Answer and explanation

Changing a subscript would change the identity of the substance itself (turning it into a different compound), but a coefficient just changes how many molecules you have of the same substance — the atoms and identity stay the same.

Problem 27

The equation CH₄ + 2O₂ → CO₂ + 2H₂O is balanced. How many total oxygen atoms are on the reactant side?
Answer and explanation

4 atoms

2 molecules of O₂ each have 2 oxygen atoms: 2 × 2 = 4 oxygen atoms.

Problem 28

Balance H₂ + O₂ → H₂O and verify each element. Explain the reasoning in your own words.
Answer and explanation

2H₂ + O₂ → 2H₂O; H=4 and O=2 on each side.

Put 2 before H₂O to give two oxygen atoms on the right.

Put 2 before H₂ so both sides contain four hydrogen atoms.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 29

Balance Mg + O₂ → MgO and verify atom counts. Show the reasoning, not just the conclusion.
Hints

Totals of molecules differ, but each element's atom count matches.

Answer and explanation

2Mg + O₂ → 2MgO. Both sides contain 2 Mg and 2 O atoms.

Problem 30

Does 2H₂ + O₂ → 2H₂O require equal molecule counts on both sides? Explain.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. There are 3 reactant molecules and 2 product molecules in the ratio, but 4 H and 2 O atoms on each side.

Problem 31

Balance counts by changing whole-particle coefficientsBalance counts by changing whole-particle coefficientsUnbalanced: H₂ + O₂ → H₂OLeft: H 2, O 2. Right: H 2, O 1.Balanced: 2H₂ + O₂ → 2H₂OLeft: H 4, O 2. Right: H 4, O 2.A coefficient counts whole molecules. Changing H₂O to H₂O₂ changes identity.
The first specified water equation has unequal oxygen counts. The balanced form uses coefficients 2, 1 and 2 to preserve four H atoms and two O atoms. Subscripts remain unchanged because they describe each substance. An equation arrow describes the chemical account; it is not a physical force or motion arrow.
For this unit’s illustrated case, why must adding 2 before H₂O also be followed by changing the H₂ coefficient?
Answer and explanation

Two H₂O molecules contain four H atoms, so two H₂ reactant molecules are needed to match them. The O₂ molecule already supplies the two O atoms.

A coefficient multiplies every atom in a formula. Recount all elements after each change, including an element that was previously balanced. This prevents solving the oxygen mismatch by accidentally creating a hydrogen mismatch.

Two H₂O molecules contain four H atoms, so two H₂ reactant molecules are needed to match them. The O₂ molecule already supplies the two O atoms.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 32

For the supplied reaction N₂ + H₂ → NH₃, keep all formulas unchanged and find the simplest whole-number coefficients. Check both element counts.
Answer and explanation

N₂ + 3H₂ → 2NH₃. Both sides contain 2 N atoms and 6 H atoms.

Match two nitrogen atoms using 2NH₃.

That product count needs six H atoms, supplied by 3H₂.

N₂ + 3H₂ → 2NH₃. Both sides contain 2 N atoms and 6 H atoms.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 33

In an exothermic reaction, energy is…
  1. absorbed from the surroundings, cooling them
  2. released to the surroundings, warming them
  3. destroyed completely
  4. only stored, never released
Answer and explanation

released to the surroundings, warming them

Exothermic reactions release energy outward to the surroundings, which is why they feel warm.

Problem 34

A beaker of water at 24°C is used in a reaction. Afterward, the water measures 31°C. What is the temperature change, ΔT?
Answer and explanation

7 °C

ΔT = 31°C − 24°C = 7°C. The rise in temperature suggests an exothermic reaction.

Problem 35

Which of these is an example of an endothermic process?
  1. wood burning in a campfire
  2. an instant cold pack activating
  3. natural gas burning on a stove
  4. fireworks exploding
Answer and explanation

an instant cold pack activating

A cold pack absorbs heat from its surroundings to feel cold, which is endothermic.

Problem 36

A chemical reaction absorbs heat from surrounding water while forming new substances. Is it endothermic or exothermic? Explain using the reacting chemicals as the system.
Answer and explanation

Endothermic: the reacting chemical system takes energy as heat from the surroundings overall. Surrounding water can cool if other energy transfers are controlled.

Problem 37

A hand warmer raises the temperature of the air around it from 18°C to 42°C. What is ΔT?
Answer and explanation

24 °C

ΔT = 42°C − 18°C = 24°C.

Problem 38

A cold-pack process cools its surrounding water from 22°C to 15°C. Describe the direction of energy transfer. Explain the reasoning in your own words.
Answer and explanation

Energy entered the pack process; the process is endothermic under these conditions.

The surroundings lost thermal energy as they cooled.

The pack's process absorbed energy from those surroundings.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 39

A process lowers surrounding water from 24°C to 17°C. Classify it and justify your boundary. Show the reasoning, not just the conclusion.
Hints

State the system boundary before naming the direction.

Answer and explanation

Endothermic for the process: it takes energy from the water, which cools.

Problem 40

A process is exothermic but a poorly insulated cup shows little warming. Explain a possible reason.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Released energy may transfer to the room or container instead of remaining in the measured water; a small temperature rise alone does not measure all energy released.

Problem 41

Using the source table, choose a qualifying design, draw the containment/transfer model and justify one revision. Explain what a new test must measure and why selecting only the hottest design can fail. Complete either the supervised small-scale cooler construction/retest or the supplied-data design route. State which route you used and submit its matching evidence; do not claim actual construction from a paper model.
Hints

Use the illustrated study titled Design a chemical thermal device. Keep the observations, model and conditions separate.

Answer and explanation

A qualifies at 32 °C under the stated 40 °C maximum, while B’s 45 °C violates it despite longer duration. A revision could improve insulation or transfer geometry within the reagent limit, then retest target temperature over time and check containment. Supplied C records at 35 °C for 12 minutes support that simulated comparison; they do not substitute for actual construction evidence. Account for reaction, target and surrounding energy pathways. For a real cooler route, vinegar/bicarbonate interaction can lower the reaction-mixture temperature; target water can then transfer energy through the inner-cup wall. Record the target separately and compare repeated A/B curves with a no-reaction reference. Geometry and environmental exchange can obscure a small effect, so no precise decrease is promised. A model or example result is not a substitute for actual target readings.

A qualifies at 32 °C under the stated 40 °C maximum, while B’s 45 °C violates it despite longer duration. A revision could improve insulation or transfer geometry within the reagent limit, then retest target temperature over time and check containment. Supplied C records at 35 °C for 12 minutes support that simulated comparison; they do not substitute for actual construction evidence. Account for reaction, target and surrounding energy pathways. For a real cooler route, vinegar/bicarbonate interaction can lower the reaction-mixture temperature; target water can then transfer energy through the inner-cup wall. Record the target separately and compare repeated A/B curves with a no-reaction reference. Geometry and environmental exchange can obscure a small effect, so no precise decrease is promised. A model or example result is not a substitute for actual target readings.

Response criteria

  • Apply criteria and hard constraints.
  • Explain reaction energy, separate target/mixture readings and open containment.
  • Compare original/revised trial evidence and its limits.

Problem 42

Define the system before naming the energy-transfer directionDefine the system before naming the energy-transfer directionDefined reaction systemSpecified processExothermic: net outwardEndothermic: net inwardThe two arrows are separate alternative cases, not simultaneous net transfers.The same surroundings can include the container, water and nearby air.
The box marks a chosen reaction-system boundary. Two alternative supplied cases show net energy transfer outward for an exothermic process and inward for an endothermic process. These opposite alternatives do not mean the same reaction has both net classifications at once. Naming the surroundings makes the account explicit before discussing measured temperature or bond changes.
For this unit’s illustrated case, for the endothermic alternative, which side supplies net energy and why could the monitored surroundings cool?
Answer and explanation

Energy comes from the surroundings into the defined system overall. The surroundings can cool as they transfer energy, depending on the actual mass and other transfer paths.

A system is the chosen objects or process being studied. Surroundings are the interacting objects outside that boundary. Exothermic and endothermic name net transfer directions, so identify the boundary and interval first.

Energy comes from the surroundings into the defined system overall. The surroundings can cool as they transfer energy, depending on the actual mass and other transfer paths.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 43

A specified process needs 80 model energy-units for bond breaking and releases 55 through bond formation. Find the net requirement and explain why bond formation itself is not the energy-requiring step.
Answer and explanation

Net 25 units enter from surroundings under this model, so the overall reaction is endothermic. Forming bonds releases 55; breaking them requires 80.

Compare the two contributions with directions stated.

Classify the net result, not an isolated bond step.

Net 25 units enter from surroundings under this model, so the overall reaction is endothermic. Forming bonds releases 55; breaking them requires 80.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 44

A substance with a pH of 10 is…
  1. strongly acidic
  2. neutral
  3. basic
  4. impossible, since pH can't exceed 7
Answer and explanation

basic

A pH above 7 is basic; 10 is well above 7.

Problem 45

Pure water has a pH of ___.
Answer and explanation

7

Pure water sits exactly at the neutral point, pH 7.

Problem 46

Which everyday substance is most likely a strong base?
  1. orange juice (pH ≈ 3.5)
  2. black coffee (pH ≈ 5)
  3. drain cleaner (pH ≈ 13)
  4. milk (pH ≈ 6.5)
Answer and explanation

drain cleaner (pH ≈ 13)

A pH near 13 is far above 7, making drain cleaner a strong base.

Problem 47

Explain how an indicator like litmus paper is used to test whether a solution is acidic or basic.
Answer and explanation

You dip the litmus paper into the solution; if it turns red, the solution is acidic, and if it turns blue, the solution is basic. The color change tells you the general pH range without needing a meter.

Problem 48

An acidic solution has a pH of 4. After adding a base, its pH rises by 3. What is the new pH?
Answer and explanation

7

New pH = 4 + 3 = 7, which is neutral.

Problem 49

Mixing an acid and a base together in a neutralization reaction produces water and a…
  1. gas only
  2. salt
  3. new acid
  4. new base
Answer and explanation

salt

Neutralization reactions between an acid and a base produce water plus a salt.

Problem 50

Compare the hydrogen-ion activity in solutions of pH 3 and pH 5. Explain the reasoning in your own words.
Answer and explanation

The pH 3 solution has about 100 times the hydrogen-ion activity of pH 5 under comparable conditions.

The pH difference is 5−3=2.

Each step is a factor of 10, so the factor is 10×10=100.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 51

Compare hydrogen-ion activity at pH 5 and pH 6. Show the reasoning, not just the conclusion.
Hints

A lower pH must correspond to greater, not smaller, hydrogen-ion activity.

Answer and explanation

The pH 5 sample has 10 times the activity, because the difference is one logarithmic unit.

Problem 52

Can two solutions with equal pH always be treated as equally safe? Explain.
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Toxicity, concentration, total amount, chemical identity and exposure also matter; pH is only one property.

Problem 53

An indicator color estimates a range with uncertaintyAn indicator color estimates a range with uncertaintyReading 1Reading 2Reading 3Key: pH 5–6Key: pH 5–6Unclear matchSupplied indicator key only: color means a range, not an exact decimal.Compare fresh samples, consistent lighting and the correct reference chart.
Two illustrative test colors match the supplied pH 5–6 key while a third reading is ambiguous. These colors are a specific provided key, not a universal rule for every indicator. An indicator’s transition range, lighting, amount and sample color can limit the estimate. No taste, skin test or mixing of unknown chemicals is intended.
For this unit’s illustrated case, what pH claim is supported, and why would reporting 5.34 be unjustified?
Answer and explanation

A range around pH 5–6 is supported by the two clear matches, with the ambiguous result noted. The color method does not supply precision to two decimal places.

A range expresses what the method can resolve. Repeat a consistent approved measurement and compare the actual key. Record the uncertain match instead of forcing every reading into a precise number.

A range around pH 5–6 is supported by the two clear matches, with the ambiguous result noted. The color method does not supply precision to two decimal places.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 54

A supplied indicator key gives a pH range 8–9 for a sample. Compare it qualitatively with a pH 6 sample and explain why the range does not support an exact pH 8.37 claim.
Answer and explanation

The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.

Use the supplied key and conditions.

Respect measurement resolution and the logarithmic scale.

The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Browse all courses