4.2 reactions of acids

Question 1

Which ion do acids produce in aqueous solution?

Answer 1

H+

Question 2

Acids react with alkalis.
What is the name of this type of reaction?

Answer 2

neutralisation

Question 3

The 25 cm3 of potassium hydroxide solution is measured with the
measuring cylinder.
Which piece of equipment could the student use to measure the 25 cm3 of
potassium hydroxide solution more accurately?

Answer 3

pipette

Question 4

Describe how the student would use the equipment in the figure above to
complete the titration

Answer 4

add potassium hydroxide (solution) to the (conical) flask

add (a few drops of) indicator

add the (sulfuric) acid (from the burette)

until the colour (of the indicator) changes

read the volume from the burette

Question 5

Why was the solution heated gently in step 3

Answer 5

to evaporate water

Question 6

Name the salt produced by the neutralisation of hydrochloric acid with
potassium hydroxide.

Answer 6

potassium chloride

Question 7

Write an ionic equation for the neutralisation of hydrochloric acid with
potassium hydroxide

Answer 7

H+ + OH− → H2O

Question 8

Copper, copper carbonate and copper oxide are insoluble solids.
Which of these insoluble solids can be used to make a copper salt by
reacting the solid with dilute hydrochloric acid?

Answer 8

copper carbonate and copper oxide only

Question 9

when making crystals of magnesium sulfate, why warm the sulfuric acid

Answer 9

to speed up the reaction

Question 10

why repeat steps until there’s magnesium oxide remaining in the beaker when making crystals of magnesium sulfate

Answer 10

to make sure all the acid reacts

Question 11

why would you filter the mixture when making crystals of magnesium sulfate

Answer 11

to remove the excess magnesium oxide

Question 12

Hydrogen chloride and ethanoic acid both dissolve in water.
All hydrogen chloride molecules ionise in water.
Approximately 1% of ethanoic acid molecules ionise in water.

(a) A solution is made by dissolving 1 g of hydrogen chloride in 1 dm3 of water. What is the correct description of this solution?

Answer 12

A dilute solution of a weak acid

Question 13

A student investigated the concentration of a solution of sodium hydroxide by
titration with a 0.0480 mol/dm3 ethanedioic acid solution.

Suggest two general improvements that would increase the
accuracy of the result

Answer 13

• swirl (the solution)
• white tile (under the flask)
• add (ethanedioic) acid dropwise (near the endpoint)
• repeat and calculate mean

Question 14

Which is a base the student could use to produce zinc nitrate?

Answer 14

Zinc oxide

Question 15

Name the salt with the formula MgBr2

Answer 15

magnesium bromide

Question 16

Give one advantage of using a pipette rather than using a measuring
cylinder to measure the volume of hydrochloric acid

Answer 16

(pipette) measures volume more accurately

Question 17

Complete the word equation for the reaction.
calcium hydroxide + ________________ acid → calcium chloride + ________________

Answer 17

hydrochloric

water

Question 18

The student tested two samples of dilute sulfuric acid, P and Q.
Describe how the student could use titrations to find which sample, P or Q,
is more concentrated

Answer 18

• measure the volume of acid
• add indicator to the acid
• add sodium hydroxide solution
• until the colour changes
• record volume of sodium hydroxide solution added
• repeat procedure with the other acid
• compare the two volumes of sodium hydroxide solution to find
  which sample P or Q is more concentrated* pipette to measure volume of acid
• use a few drops of indicator
• swirl
• use a white tile
• rough titration to find approximate end point
• add dropwise near the endpoint
• read volume from bottom of meniscus
• repeat and take a mean

Question 19

Calcium nitrate contains the ions Ca2+ and NO3
−
Give the formula of calcium nitrate.

Answer 19

Ca(NO3)2

Question 20

Describe a method to make pure, dry crystals of magnesium sulfate from a
metal oxide and a dilute acid.

Answer 20

• use magnesium oxide and sulfuric acid
• add sulfuric acid to a beaker
• warm sulfuric acid
• add magnesium oxide
• stir
• continue adding until magnesium oxide is in excess
• filter
• using a filter paper and funnel
• to remove excess magnesium oxide
• heat solution in an evaporating basin
• to crystallisation point
• leave to crystallise
• pat dry with filter paper

Question 21

Explain why an acid can be described as both strong and dilute.

Answer 21

(strong because) completely ionised
(dilute because) small amount of acid per unit volume

Question 22

Explain why the student should use a pipette to measure the dilute sulfuric
acid and a burette to measure the sodium hydroxide solution.

Answer 22

pipette measures a fixed volume (accurately)

(but) burette measures variable volume

Question 23

describe a method to find the exact volume of sodium hydroxide that reacts with 25 cm3 of hydrochloric acid

Answer 23

fill burette with sodium hydroxide

add sodium hydroxide from the burette to the hydrochloric acid and
indicator

stop when colour changes

measure volume used from burette

Question 24

Suggest how the student could improve Step 3 of the method to obtain
larger crystals instead of powder.

Answer 24

heat with an electric heater

Question 25

Explain why the scientist adds excess zinc rather than excess iodine.

Answer 25

to make sure that all the iodine reacts (as) excess iodine would remain in solution (so) iodine could not be filtered off

Question 26

Suggest one reason why the percentage yield in this reaction is not 100%

Answer 26

some product lost on separation

Question 27

A student titrated citric acid with sodium hydroxide solution. This is the method used. 1. Pipette 25.0 cm3 of sodium hydroxide solution into a conical flask. 2. Add a few drops of thymol blue indicator to the sodium hydroxide solution. Thymol blue is blue in alkali and yellow in acid. 3. Add citric acid solution from a burette until the end-point was reached. (b) Explain what would happen at the end-point of this titration.

Answer 27

indicator changes colour from blue to yellow (when) the acid and alkali are (exactly) neutralised

Question 28

The student repeated the experiment with potassium carbonate. The limewater did not bubble. Suggest why there were no bubbles in the limewater.

Answer 28

Potassium carbonate does not decompose to produce carbon dioxide

Question 29

Compare the atom economies of the two reactions for making copper chloride. Give a reason for the difference

Answer 29

atom economy using carbonate lower because an additional product is made or carbon dioxide is made as well

Question 30

Identify the error in the way the student set up the apparatus. Describe what would happen if the student used the apparatus shown.

Answer 30

(delivery) tube sticks into the acid the acid would go into the water

Question 31

suggest what may have happened to cause this anomalous result in collecting gas experiment

Answer 31

* bung not put in firmly / properly * gas lost before bung put in * leak from tube

Question 32

Why does the volume of carbon dioxide collected stop increasing at 95.0 cm3?

Answer 32

all of the acid has reacted

Question 33

What further work could the student do to be more certain about the minimum mass of sodium carbonate needed to produce 95.0 cm3 of carbon dioxide

Answer 33

take more readings in range 0.34 g to 0.54 g

Question 34

One student said that the results of the experiment were wrong because the first few bubbles of gas collected were air. A second student said this would make no difference to the results. whys student 2 right

Answer 34

they should be collected because carbon dioxide is left in flask at end and it has the same volume as the air collected / displaced

Question 35

Explain, in terms of particles, how and why the rate of reaction changes during the reaction of calcium carbonate with hydrochloric acid

Answer 35

acid particles used up so concentration decreases so less frequent collisions so rate decreases

Question 36

simple titration:

Answer 36

* acid in burette or flask * alkali/sodium hydroxide or acid in burette or flask * volume of acid or alkali measured using the pipette * indicator in flask * white tile under the flask * slow addition * swirling/mixing * colour change of indicator * burette volume measured