4.2 reactions of acids Flashcards
Which ion do acids produce in aqueous solution?
H+
Acids react with alkalis.
What is the name of this type of reaction?
neutralisation
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?
pipette
Describe how the student would use the equipment in the figure above to
complete the titration
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
Why was the solution heated gently in step 3
to evaporate water
Name the salt produced by the neutralisation of hydrochloric acid with
potassium hydroxide.
potassium chloride
Write an ionic equation for the neutralisation of hydrochloric acid with
potassium hydroxide
H+ + OH− → H2O
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?
copper carbonate and copper oxide only
when making crystals of magnesium sulfate, why warm the sulfuric acid
to speed up the reaction
why repeat steps until there’s magnesium oxide remaining in the beaker when making crystals of magnesium sulfate
to make sure all the acid reacts
why would you filter the mixture when making crystals of magnesium sulfate
to remove the excess magnesium oxide
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?
A dilute solution of a weak acid
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
- swirl (the solution)
- white tile (under the flask)
- add (ethanedioic) acid dropwise (near the endpoint)
- repeat and calculate mean
Which is a base the student could use to produce zinc nitrate?
Zinc oxide
Name the salt with the formula MgBr2
magnesium bromide
Give one advantage of using a pipette rather than using a measuring
cylinder to measure the volume of hydrochloric acid
(pipette) measures volume more accurately
Complete the word equation for the reaction.
calcium hydroxide + ________________ acid → calcium chloride + ________________
hydrochloric
water
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
- 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
Calcium nitrate contains the ions Ca2+ and NO3
−
Give the formula of calcium nitrate.
Ca(NO3)2
Describe a method to make pure, dry crystals of magnesium sulfate from a
metal oxide and a dilute acid.
- 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
Explain why an acid can be described as both strong and dilute.
(strong because) completely ionised
(dilute because) small amount of acid per unit volume
Explain why the student should use a pipette to measure the dilute sulfuric
acid and a burette to measure the sodium hydroxide solution.
pipette measures a fixed volume (accurately)
(but) burette measures variable volume
describe a method to find the exact volume of sodium hydroxide that reacts with 25 cm3 of hydrochloric acid
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
Suggest how the student could improve Step 3 of the method to obtain
larger crystals instead of powder.
heat with an electric heater
Explain why the scientist adds excess zinc rather than excess iodine.
to make sure that all the iodine reacts
(as) excess iodine would remain in solution
(so) iodine could not be filtered off
Suggest one reason why the percentage yield in this reaction is not
100%
some product lost on separation
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.
indicator changes colour
from blue to yellow
(when) the acid and alkali are (exactly) neutralised
The student repeated the experiment with potassium carbonate.
The limewater did not bubble.
Suggest why there were no bubbles in the limewater.
Potassium carbonate does not decompose to produce carbon
dioxide
Compare the atom economies of the two reactions for making copper
chloride.
Give a reason for the difference
atom economy using carbonate lower because an additional product is
made or carbon dioxide is made as well
Identify the error in the way the student set up the apparatus.
Describe what would happen if the student used the apparatus shown.
(delivery) tube sticks into the acid
the acid would go into the water
suggest what may have happened to cause this anomalous result in collecting gas experiment
- bung not put in firmly / properly
- gas lost before bung put in
- leak from tube
Why does the volume of carbon dioxide collected stop increasing at 95.0
cm3?
all of the acid has reacted
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
take more readings in range 0.34 g to 0.54 g
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
they should be collected because carbon dioxide is left in flask at end
and it has the same volume as the air collected / displaced
Explain, in terms of particles, how and why the rate of reaction changes
during the reaction of calcium carbonate with hydrochloric acid
acid particles used up
so concentration decreases
so less frequent collisions
so rate decreases
simple titration:
- 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
