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chemistry > Topic 11 - Acids > Flashcards

Topic 11 - Acids Flashcards

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1
Q

PH of..
1. A strong acid
2. A weak alkali
3. A neutral substance
4. A strong alkali
5. A weak acid

A
  1. 1-2
  2. 8-10
  3. 7
  4. 13-14
  5. 4-6
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2
Q

What do acids all contain?

A

All acids contain hydrogen atoms. When acids dissolve in water to form H+ ions. The more concentrated the H+ ions the lower the PH of the acid.

HCl - Hydrochloric acid HCl —> H+ + Cl-
In water hydrochloric acid separates into H+ and Cl- ions
H2So4 - sulfuric acid H2So4 —> 2H+ + So4^2-
HNo3 - Nitric acid —> HNo3 —> H+ + No3-

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3
Q

What do alkalines all contain?

A

All alkaline solutions contain hydroxide ions (OH-). The more concentrated the OH- ions the higher the PH of the alkali.

NaOH - Sodium hydroxide NaOH —> Na+ + OH-
Ca(OH)2 - Calcium hydroxide Ca(OH)2 —> Ca2+ + 2OH-
KOH - Potassium hydroxide KOH —> K+ + OH-

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4
Q

What are the 3 indicators?

A

Litmus
Methyl orange
Phenolphthalein

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5
Q

What impact do acids and alkalis have on litmus?

A

Acids: Red
Alkali: Blue

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6
Q

What impact do acids and alkalis have on methyl orange?

A

Acids: Red
Alkalis: Yellow

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7
Q

What impact do acids and alkalis have on phenolphthalein?

A

Acids: Colourless
Alkalis: Pink

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8
Q

Concentration

A

How concentrated a substance is depends on how many particles are dissolved in a set volume.

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9
Q

Concentrated acids

A

Have a lot of acid particles dissolved in water.

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10
Q

Dilute acids

A

Only have a few acid particles dissolved in water.

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11
Q

What does 1 dm3 = in cm3

A

1000 cm3

Cm3 —> dm3 /1000
Dm3 —> cm3 X 1000

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12
Q

Concentration

A

Mass/Volume
g/dm3

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13
Q

Strong acids

A

Completely dissociate into ions in water/solution.

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14
Q

Weak acids

A

Only partially dissociate into ions in water/solution.

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15
Q

What is PH a measure of

A

• The concentration of H+ in a solution.
• The lower the PH, the more concentrated the H+ solution.
• The concentration of H+ depends on the concentration and strength of the acid.
Each PH change means a H+ concentration change by a factor of 10.

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16
Q

Base

A

A base is a substance that can neutralise acids to form salt and water only.

Metal oxides and metal hydroxides are bases.

17
Q

Salt

A

A salt is a substance made from an acid, where the hydrogen ion (H+) has been swapped with a metal ion.

18
Q

Alkali

A

An alkali is a base dissolved in water.

19
Q

Neutralisation

A

A neutralisation reaction is when an acid reacts with a base (or alkali) to form a salt and water.

20
Q

Acids and metal types

A

Hydrochloric acid (HCl) = metal chloride
Sulfuric acid (H2SO4) = metal sulfate
Nitric acid (HNO3) = metal nitrate

21
Q

Core practical:
Neutralisation

A
  1. Fill beaker with 50cm3 of hydrochloric acid.
  2. Dip a glass rod into the acid and put onto universal indicator paper. Wait 30 seconds and record the PH of the acid. Wash the glass rod.
  3. Measure 0.3G of calcium hydroxide using a weighing boat.
  4. Add calcium hydroxide to acid and stir.
  5. Measure the PH of the mixture. Wash the glass rod.
  6. Repeat steps 3-5 until you have added a total of 2.4g to the acid.
22
Q

How to measure PH more accurately?

A

• Use a PH metre.

23
Q

How to improve method?

A

Use smaller mass intervals each time.

24
Q

Preparing copper sulphate core practical

A
  1. Add 20cm3 sulfuric acid to a beaker.
  2. Warm gently - do not boil. Turn off Bunsen burner.
  3. Add excess copper oxide and stir.
  4. Filter excess copper oxide from copper sulfate solution.
  5. Gently heat solution in an evaporating basing using a water back for 3 minutes - do not boil dry.
  6. Place the evaporating basin in a warm place and leave to continue to dry.
25
Q

Core practical key points

A

• Add excess copper oxide to make sure all the acid reacts.
• Copper oxide is insoluble so gets stuck in the filter paper. Copper sulfate is soluble so dissolves and goes through.
• A water bath is used because it heats more accurately than a Bunsen burner so that it doesn’t dry and forms bigger crystals.

26
Q

Acid-alkali neutralisation

A

A reaction in which hydrogen ions (H+) from the acid react with hydroxide ions (OH-) from the alkali to make water (H2O).

27
Q

Titration core practical method

A

• Measure out a set amount of acid into a conical flask using a pipette. Add a few drops of indicator.
• Slowly add alkali to the acid, using a burette, until you reach the need point - this is when the acids been exactly neutralised and the indicator changes colour.
• Then carry out the reaction using exactly the same columns of acids and alkalis but without the indicator, so the salt won’t be contaminated with indicator.
• The solution that remains when the reaction is complete contains only salt and water.
• Slowly evaporate off some of the water and then leave the solution to crystallise. Filter off the solid and dry it - You will be left with a pure dry salt.

28
Q

Why must titration be used?

A

You need to work out exactly the right amount of alkali to neutralise the acid. So you need to do a titration using an indicator.

29
Q

Why are the acid and soluble reactant mixed in the same proportions?

A

You can’t add an excess of alkali to the acid because the salt is soluble and would be contaminated with the excess alkali.

30
Q

Titration

A
  1. Measure 25cm3 of sodium hydroxide in a pipette.
  2. Move it into a conical flask.
  3. Add 3 drops of indicator.
  4. Make sure the tap on the berrete us closed.
  5. Fill it to 0cm3 with hydrochloric acid.
  6. Add the hydrochloric acid and swirl until colour change.
  7. Measure and record volume used.
  8. Repeat steps 1-8 but add drop wise near the end point until you have Concordant data.
  9. To make the pure salt, repeat the steps to add the exact amount of hydrochloric acid to 25cm3 of sodium hydroxide without indicator.
31
Q

Preparing an insoluble salt

A
  1. Add soluble salts to water and mix.
  2. Filter to remove precipitate from the mixture.
  3. Wash the precipitate with distilled water to remove traces of solution.
  4. Dry the precipitate.
32
Q

Which hydroxides are soluble?

A

Sodium, potassium, ammonium.

33
Q

Which carbonates are soluble?

A

Sodium, potassium, ammonium.

34
Q

Which sulfate are insoluble?

A

Lead, barium, calcium

35
Q

Which chlorides are insoluble?

A

Silver, lead.

chemistry (13 decks)

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