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A measuring cylinder contains 25 mL of water. After a small food sample is fully submerged, the reading is 32 mL. Which result is correct? Assume the sample is fully submerged without air bubbles and does not absorb or dissolve in the water.
A measuring cylinder was used, and the sample volume is 7 mL. A balance was used, and the sample volume is 7 g. A measuring cylinder was used, and the sample volume is 32 mL. A measuring cylinder was used, and the sample volume is 25 mL. Salt is mixed with insoluble ground pepper. Which sequence recovers the salt?
Add water to dissolve the salt, filter off the pepper, then evaporate water from the filtrate. Add water, then filter because the dissolved salt will remain on the filter paper. Add water, keep only the pepper, and discard the liquid because dissolved salt no longer exists. Evaporate the dry mixture first, then use dissolving and filtration in any order. A kitchen needs liquid water from salt water and must check whether a colouring contains several soluble dyes. Which methods fit both everyday tasks?
Distil the salt water to condense and collect water; use paper chromatography to separate the dyes into spots. Let the water evaporate without condensing it; use paper chromatography for the dyes. Distil the mixture by collecting only the dry salt; filter the dissolved dyes through paper. Filter the salt water, then use chromatography because dyes differ only in particle size. Which account correctly identifies chemical change and ways to slow unwanted reactions in food contexts?
Evidence of new products supports a chemical reaction; preservation slows decay, reducing cooker fuel can slow cooking, reducing fuel or oxygen can slow burning, and intact tin plating slows rusting. Any visible change alone proves a chemical reaction; the three slowing methods are otherwise correctly described. Preservation permanently prevents every future decay reaction; the other statements are correct. Intact tin plating is intended to make iron rust faster; the other statements are correct. Which row correctly compares litmus, universal indicator, a pH meter and the pH scale?
Litmus distinguishes acidic and alkaline behaviour; universal indicator estimates pH from a colour scale; a pH meter gives a number; values below 7 are acidic and above 7 are alkaline. Litmus gives an exact numerical pH; the other descriptions are correct. A pH meter must be matched to a colour chart; the other descriptions are correct. Values below 7 are alkaline and values above 7 are acidic; the tool descriptions are correct. Which row gives the general products for three acid reactions and identifies neutralisation?
Acid + metal: salt and hydrogen; acid + base: salt and water only; acid + carbonate: salt, water and carbon dioxide; acid + base is neutralisation. Acid + metal produces salt and carbon dioxide; the other reaction patterns are correct. Acid + base produces salt and hydrogen; the other reaction patterns are correct. Acid + carbonate produces salt, water and hydrogen; the other reaction patterns are correct.
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A recipe requires 46 mL of cooking oil. Which instrument and quantity should the learner use?
Use a measuring cylinder and measure to the 46 mL mark. Use a balance and measure to the 46 mL mark. Use filter paper because filtration measures liquid volume. Use a pH meter because every numerical reading is a volume. A fruit piece raises water in a measuring cylinder from 41 mL to 55 mL. A separate juice sample contains insoluble pulp. Which result and method are correct? Assume the sample is fully submerged without air bubbles and does not absorb or dissolve in the water.
The fruit volume is 14 mL, and filtration removes the pulp. The fruit volume is 55 mL, and evaporation removes the pulp. The fruit volume is 41 mL, and distillation removes the pulp. The fruit mass is 14 g, and dissolved pulp is trapped by filtration. Equal bread samples are stored for six days. The refrigerated sample develops fewer new odour-producing substances than the room-temperature sample. Which conclusion is supported?
Formation of new substances is evidence of chemical decay, and refrigeration slowed that decay under the tested conditions. Any change in appearance alone proves chemical decay, and refrigeration permanently stopped every future reaction. Refrigeration sped decay because fewer new substances appeared in the refrigerated sample. No chemical change can occur in food because temperature changes are always physical changes. Acid added to magnesium produces a gas that burns with a pop. The same acid added to a carbonate produces a gas that turns limewater milky. Which products explain the gas tests?
The metal reaction forms salt and hydrogen; the carbonate reaction forms salt, water and carbon dioxide. The metal reaction forms carbon dioxide, while the carbonate reaction forms hydrogen. Both reactions form only salt and water, so neither observation can involve a gas. Both reactions form hydrogen because every acid reaction produces the same gas. Which choice correctly distinguishes evaporation from distillation for salt water?
Evaporation collects water; distillation collects only dry salt. Both methods collect water without any condensation. Both methods remove dissolved salt with filter paper. Evaporation can recover salt; distillation can collect water. A gas cooker flame is turned down using its fuel control. Why can food in the pan cook more slowly?
The reduced fuel supply slows the cooking reaction. More fuel is supplied, so cooking slows. More oxygen is supplied, so every reaction stops. Turning down fuel proves no new products can ever form. Which treatment is named for slowing rusting of iron food cans?
Increase fuel supply around the can. Cover the iron with an intact tin plating. Scratch away the tin to expose the iron. Add tin so the iron reacts faster. A learner needs an estimated pH range from an indicator. Which tool and reading should be used?
Universal indicator and its pH colour chart. Litmus and an exact numerical display. A pH meter and a paper colour chart only. Universal indicator with only a yes-or-no acid result. A drink has pH 3. How should it be classified?
Acidic. Neutral, because every drink has pH 7. Alkaline, because low pH means alkali. Unclassifiable because pH values do not show acidity. Which word pattern describes an acid reacting completely with a suitable base in neutralisation?
Acid plus base forms carbon dioxide only. Acid plus base must leave an acidic product. Acid plus base forms salt and water only. Acid plus base forms salt and hydrogen. A sample contains soluble sugar crystals mixed with insoluble sand. Which plan recovers the sand first and also keeps the sugar available for later recovery?
Add water and pour the whole suspension through without filter paper, then discard both portions. Add water to dissolve the sugar, filter to collect and wash the sand, and retain the filtrate for evaporation. Filter the dry mixture before adding water and discard everything that passes through. Add water, evaporate the mixture to dryness immediately, and call the remaining mixed solid pure sand. A black food colouring forms three separated spots after chromatography, while a reference blue dye forms one spot at the same height as one of them. What can be concluded?
The black colouring contains at least three components, including a component consistent with the reference blue dye under these conditions. The black colouring is a pure substance because all three spots began at one origin line. The reference dye must contain all three black-colouring components because one spot matches. Chromatography can only separate insoluble solids, so the spots provide no compositional evidence. Magnesium is added to dilute hydrochloric acid and a colourless gas is collected. Which product account and test are consistent with the reaction?
A salt and carbon dioxide form; limewater must turn milky. A salt and oxygen form; a glowing splint must relight. No new substances form; the gas is only trapped air escaping. A salt and hydrogen form; a lighted splint at the gas gives a squeaky pop.
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A learner says a grape has volume 27 mL because the cylinder reads 18 mL before submersion and 27 mL after. Which correction is valid? Assume the sample is fully submerged without air bubbles and does not absorb or dissolve in the water.
The grape volume is 9 mL because its displaced volume is 27 mL − 18 mL. The grape volume is 27 mL because only the final reading matters. The grape volume is 18 mL because the first reading is its volume. The grape mass is 45 g because the two cylinder readings add. Salt is mixed with insoluble sand. What should be done first so the salt can later be separated from the sand?
Evaporate the dry mixture to collect water. Use chromatography because sand differs only in particle size. Add water to dissolve the salt. Filter the dry mixture to trap dissolved salt. Which method separates insoluble tea leaves from brewed tea?
Distillation, because only dissolved solids can pass a filter. Paper chromatography, because leaves differ in size. Filtration. Dissolving, because the leaves should disappear. A salt solution is heated gently and water is allowed to escape. Which substance is collected by evaporation?
Only insoluble filter residue. Separate dye spots on paper. The dissolved salt. The water as a condensed liquid. Which method should be used to obtain liquid water from seawater?
Evaporation without condensation. Filtration through paper. Dissolving the salt again. Distillation. A drink contains several soluble food colourings. Which method can show the separate colourings?
A measuring cylinder, because the colours differ only in volume. Paper chromatography. Filtration, because dissolved colours cannot pass paper. Evaporation, because the solvent must be collected. Which everyday separation is correctly matched to its method?
Obtaining water from seawater by filtration. Collecting pure water from seawater by evaporation only. Separating food dyes because they have different particle sizes only. Removing tea leaves from tea by filtration. Ice melts and later refreezes. Why is this not, by itself, evidence of a chemical reaction?
Any visible liquid proves a new product formed. Cooling always creates a different chemical substance. No new product has been formed. Every reversible change is chemical. Why is 'preserved food can never decay' an overstatement?
It slows decay; it need not stop it. Preservation is designed to speed all decay. Preservation changes food only by melting it. Preservation works by adding unlimited fuel. Which action can slow a burning fire by changing oxygen supply?
Increase the oxygen reaching the fire. Increase both oxygen and fuel to slow burning. Leave the oxygen unchanged and claim appearance alone slows it. Reduce the oxygen reaching the fire. Why can a deep scratch reduce the rust protection of a tin-plated iron can?
Exposed iron must rust more slowly because tin speeds rusting. The scratch removes oxygen from the surroundings. The scratch can expose iron where the barrier is broken. A scratch cannot affect protection at any depth. What useful property does litmus have when testing a solution?
It displays an exact numerical pH. It gives the same yes-or-no result for every solution. It measures the solution’s volume in millilitres. Its colour changes differently in acidic and alkaline solutions. Which choice correctly obtains a numerical pH reading?
A pH meter. Red litmus paper alone. A pH meter interpreted only through a colour chart. Universal indicator with no colour scale. Which pH classifications are correct?
Only litmus can classify them; pH values cannot. pH 5 acidic, pH 7 neutral, pH 10 alkaline. pH 5 alkaline, pH 7 acidic, pH 10 neutral. All three values are neutral. An acidic food contacts a reactive metal and bubbles form. Which gas fits the acid–metal pattern?
No gas, because acids never react with metals. Hydrogen. Carbon dioxide, because every acid reaction makes it. Water vapour, because the metal neutralises to water only. An alkaline antacid reduces excess stomach acidity. Which type of reaction explains this use?
An acid–carbonate reaction that can only be identified by pH colour. No reaction, because a base cannot reduce acidity. An acid–base neutralisation reaction. An acid–metal reaction that must make hydrogen. Baking soda reacts with an acidic ingredient and causes bubbles in food. Which gas matches the acid–carbonate pattern?
Hydrogen, because every acid reaction gives the same gas. No gas, because carbonates form only salt and water. Carbon dioxide. Oxygen, because every bubbling reaction releases it. A suitable acid and base react in the correct amounts. Which outcome shows neutralisation can form only the stated products?
Salt and hydrogen are formed. Water and carbon dioxide are formed. The mixture must remain acidic after reaction. Salt and water are formed.
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