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Chemistry > Topic 4: Acids And Alkalis > Flashcards

Topic 4: Acids And Alkalis Flashcards

1
Q

What is an aqueous solution?

A

A mixture that is formed when a substance is dissolved in water.

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2
Q

What is the difference between an acid and an alkali?

A

Acid: a solution that reacts with alkalis, turns litmus red and has a pH less than 7. They form H+ ions in water.

Alkali: a solution which contains excess OH- ions, turns litmus blue and has a pH greater than 7.

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3
Q

Define the term neutral:

A

A solution that is neutral has a pH of 7 and is turns green when universal indicator is added to it.

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4
Q

What are the problems with some acids and alkaline’s and how are these problems made aware to people?

A

They can be corrosive, toxic or harmful to the environment. The hazards associated with handling specific solutions are identified by international symbols. They indicate the precautions needed when handling them.

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5
Q

What is the pH scale?

A

This measure the acidity or alkalinity of a solution. The scale goes from 0-14. Above 7 means the greater the alkalinity of the solution. Below 7 means the stringer the acidity. 7 is neutral.

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6
Q

How can the pH of a solution be found?

A

Using indicators. Indicators are substances that change colour depending on the pH.

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7
Q

Why does universal indicator have a range of colours?

A

It is made from a mixture of different indicators and produces a range of colours depending on the pH.

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8
Q

What colours does litmus turn in the presence of an acid or an alkali?

A

Acid: red
Alkali:blue

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9
Q

What colours does methyl orange turn in the presence of an acid or an alkali?

A

Acid: red
Alkali: yellow

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10
Q

What colours does phenolphthalein turn in the presence of an acid or an alkali?

A

Acid: colourless
Alkali: pink

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11
Q

What is an ion and how does it form a positive or negative change?

A

An ion is an atoms that has become charged by loosing or gaining elections.

Losing electrons forms a positive charge because now there are more protons than electrons and haunting electrons forms a positive charge because there are now more electrons than protons.

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12
Q

What is a polyatomic ion and how is it formed?

A

They are formed when small groups of atoms held together by covalent bonds, lose or gain electrons. E.g OH-, NO3-, SO42-.

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13
Q

What do acids produce when the dissolve in water?

A

They produce an excess of hydrogen ions (H+) when they dissolve in water.

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14
Q

What to alkalis produce when they’re dissolved in water?

A

Excess hydroxide ions (OH-) in water.

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15
Q

What makes a concentrated acid solution?

A

The higher the number of hydrogen ions in a certain volume, the higher their concentration. The higher the concentration, the more acidic the solution and the lower the pH.

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16
Q

What makes a concentrated alkaline solution?

A

The higher the number of OH- ions (hydroxide ions) in a solution, the more alkaline the solution and the higher the pH.

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17
Q

Does a neutral solution contain hydrogen and hydroxide ions?

A

Neutral solution such as pure water have a pH of 7 and contain low equal concentrations of hydrogen ions and hydroxide ions.

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18
Q

What does the term ionise/dissociate mean?

A

Means the splitting up of a substance.

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19
Q

What is the difference between a concentrated solution and a dilute solution?

A

Concentrated solution: contains a lot of dissolved solute per unit volume.

Dilute solution: contains only a small amount of solute.

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20
Q

How can you work out the concentration of a solution in gdm3?

A

Concentration= amount dissolved (g)/volume of concentration(dm3)

1000cm3=1litre=1dm3

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21
Q

How does the pH scale show the difference in concentration of H+ ions?

A

Each time the pH scale increases by 1 the difference in concentration of H + ions multiply by 10. E.g:

A solution with a pH of 0 has a concentration of H+ ions that is 10,000 times greater than a solution with a pH of 4.

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22
Q

How does the concentration of a solution affect its rate of reaction?

A

The more concentrated a solution is (more acidic) the faster it reacts with substances.

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23
Q

What is a pH meter?

A

It is used to give more accurate measurements of the pH of a substance.

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24
Q

What is the difference between a string and weak acid?

A

Strong acids: their molecules dissociate completely into ions when they dissolve in water and produce a high concentration of hydrogen ions.

Weak acid: they do not dissociate completely into ions in solutions. Therefore they will only contain a few hydrogen ions as the rest have not dissociated.

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25
Q

Is the concentration of a substance the same as the strength of a substance?

A

No they are different things. E.g You can have a strong dilute acid and a concentrated weak acid.

26
Q

What is the difference between the strength and concentration of an acid?

A

Acid strength tells you what proportion of the acid molecules ionise in water.

Acid concentration measures how much acid there is in a litre. (How watered down it is).

CONCENTRATION DESCRIBES THE TOTAL NUMBER OF DISSOLVED ACID MOLECULES-NOT THE NUMBER OF MOLECULES THAT PRODUCE HYDROGEN IONS.

27
Q

What are bases?

A

Bases are substances that neutralise acids to form salt and water only.

Metal oxides are bases they all react with acids to produce salt and water.

28
Q

What doe neutralisation reactions produce?

A

Only salt and water. (Salt is an ionic compound).

29
Q

What does a metal and base produce? Metal + base ➡️ …+….?

A

Metal + base ➡️ salt + water

BASHO

30
Q

How does a metal oxide base when reacting with a metal make a lotion more neutral?

A

During neutralisation, hydrogen ions in the acid combine with oxide ions to form water. This removes the hydrogen ions so the pH increases in order to become more neutral.

31
Q

Give the steps in order to produce a soluble salt:

E.g Tin chloride

A

1- add excess tin chloride
2-gently warm the mixture to speed up the reaction.
3-filter remove the unreacted solid from the solution.
4-heat to evaporate water and concentrate the salt solution.
5-leave to evaporate water slowly for crystallisation to occur.

32
Q

When preparing a soluble salt why must excess of the base always be added?

A

To make sure that all the acid is used up.

33
Q

When preparing a soluble salt why must the mixture be filtered?

A

To make sure the prepared salt is pure the mixture is filtered to remove the residue (the unreacted metal oxide) from the filtrate, leaving only salt and water.

34
Q

What are the steps in preparing copper sulphate?

A

Wear eye protection.

1-measure 20cm3 of dilute sulphuric acid using a measuring cylinder and pour it into a small conical flask.
2-warm the acid in a water bath set at 50°c. Use a thermometer to measure the temperature.
3-add a little copper oxide to powder to acid and stir.
4-if all the copper oxide reacts and disappears, add a little more. Stop adding when the copper oxide is in excess and no longer reacts.
5-filter the mixture and transfer the filtrate to an evaporating basin.
6-heat evaporating basin by pacing it over a beaker of heated water with a Bunsen burner. Stop heating when crystals start to form.
7-pour solution into a watch glass and leave for a few days to allow all the alter to evaporate.

35
Q

What is the difference between a soluble base and an insoluble base?

A

An soluble base is an alkali and form alkaline solutions, with pH values above 7.

36
Q

Are metal hydroxides insoluble?

A

Most of them are.

37
Q

What do acids and metal hydroxides react to produce?

Acid + metal hydroxide ➡️ … +…?

A

Acid + metal hydroxide ➡️ salt + water

38
Q

When a metal and acid react what do they form?

Metal + acid ➡️ …+…?

A

Metal + acid ➡️ salt + hydrogen

39
Q

When acids react with metal carbonates what do they form?

Acid + metal carbonate ➡️ …+…+…?

A

Acid + metal carbonate ➡️ salt + water + carbon dioxide

40
Q

What happens to the temperature of the mixture during a neutralisation reaction?

A

It becomes warmer.

41
Q

What are the steps in investigating neutralisation?

A

Wear eye protection.

1-use a measuring cylinder to add 50cm3 of dilute HCl into a beaker.
2-estimate and record the pH of the contents of the beaker:
-put a piece of universal indicator onto a white tile.
-sip the end of a glass rod into the liquid, then tap it onto the universal indicator paper.
-water 30 seconds, the match colour to that in pH chart.
3-measure out 0.3g of calcium hydroxide powder onto a piece of paper.
4-add calcium hydroxide powder to beaker and stir. Then estimate and record pH of mixture.
5-repeat steps B-C 7x so you add a total of 2.4g of calcium hydroxide to acid.
6-plot a graph with pH on y axis and and mass of powder on x axis.

42
Q

What is the test to see if a gas is carbon dioxide?

A

Bubble carbon dioxide through limewater. If the gas is carbon dioxide it will turn the lime water cloudy.

43
Q

Why does water form during the reaction between an acid and alkali?

A

H+ + OH- ➡️ H20

Hydrogen ions from the acid react with hydroxide ions from the alkali. This produces water which is simple molecular substance containing covalent bonds.

The other ions in the reaction form a salt.

44
Q

How can you obtain a dry soluble salt from its solution?

A

Crystallisation. It is important to have a neutral solution before evaporating water, otherwise you will contaminate the salt with an excess of one reactant.

45
Q

How do you obtain a neutral solution? (What process)

A

Reacting an acid with an alkali using titration.

46
Q

What is required to make a soluble salt?

A

It requires reacting an acid with an insoluble base (not an alkali).

47
Q

How to make a pure dry salt from a titration:

A
  • carry out a titration
  • note the exact volume of acid needed to neutralise the alkali
  • use the burette to add the correct volume of acid without the indicator
  • evaporate the water from the solution formed to leave the salt behind.
48
Q

What is a titration?

A

This is when acid is added from the burette to a fixed volume of alkali in a conical flask.

Use a pipettes to measure out the alkali as it’s more accurate than a measuring cylinder. A few drops of indicator is added to the alkali in the conical flask, such as phenolphthalein. This used to know the exact drop at which the acid neutralises the alkali and their will be a colour change from pink to clear.

49
Q

What is a burette and how is it accurate?

A

The burette is a tall piece of glassware with 0.1cm3 graduations.

50
Q

Define the term effervescence:

A

The formation of gas bubbles in a liquid due to a chemical reaction occurring.

51
Q

What is the reactivity series?

A

A list of metals in order of reactivity with the most reactive at the top.

Please POTASSIUM
Stop SODIUM
Calling CALCIUM
Me MAGNESIUM
A ALUMINIUM
Careless CARBON
Zebra ZINC
Instead IRON
Try TIN
Learning LEAD
How HYDROGEN
Copper COPPER
Saves SILVER
Gold GOLD
52
Q

How does the reactivity if a metal affect how it reacts with acid?

A

Reactive metals react explosively with acid

Metals in the middle of the reactivity series react steadily

53
Q

What do all acids form in an aqueous solution and what do all alkalis form in an aqueous solution?

A

All acids form hydrogen ions (H+)

All alkalis form hydroxide ions (OH-)

54
Q

What are spectator ions?

A

Ions that do not change during a reaction. They spectate.

55
Q

What is the difference between oxidation and reduction?

A

Oxidation is the loss of electrons and reduction is the gain of electrons.

OILRIG

56
Q

What is a precipitation reaction?

A

One in which soluble substances in solutions cause an insoluble precipitate to form.

57
Q

What substances are soluble and insoluble in water?

Summary

A

Soluble in water:

  • All common sodium, potassium and ammonium salts.
  • all nitrates
  • most chlorides
  • most sulphate
  • sodium, potassium as ammonium carbonates
  • sodium, potassium as ammonium hydroxides

Insoluble in water:

  • silver and lead chlorides
  • lead, barium and calcium sulphates
  • most carbonates
  • most hydroxides
58
Q

What happens when two solutions containing soluble salts react?

A

The iron from the salts swap.

59
Q

How can we predict whether a predicate will form?

A

We can predict whether a precipitate will form by checking the solubilities of the products. If both products are soluble, no precipitate will form.

60
Q

What are the steps in preparing insoluble salts?

E.g sodium nitrate

A

A pure dry sample of insoluble salt can be prepared from 2 soluble salts.

  • wear eye protection
  • mix the 2 solutions in a beaker, then filter the mixture
  • rinse the beaker with a little distilled water and pour this through the funnel.
  • pour a little distilled water over the precipitate in the funnel.
  • carefully remove the filter paper containing the precipitate and dry it in a warm oven.

Chemistry (14 decks)

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