DONT STUDY THIS Flashcards
What is an acid in regards to pH?
substance with ph less than 7
What ions do acids form in water?
H^+ ions
What can we say about concentration of hydrogen ions in a solution compared to acidity and pH?
The higher concentration of hydrogen ions in the solution, the more acidic it is, the lower the pH is
What is a base?
A substance that reacts with an acid to produce a salt and water
What is an alkali?
A base that is soluble in water
What pH do alkalis have?
Greater than 7
What ions do alkalis form in water?
OH^- ions (hydroxide ions)
What can we say about concentration of hydroxide ions in a alkaline solution compared to pH?
Higher concentration of OH^- ions, higher the pH
What is an Indictator?
A dye that changes colour depending on whether it’s above or below a certain pH
How do you use an indicator?
Add a few drops to the solution you’re testing, and compare the colour the solution goes to the pH chart for that indicator
Universal indicator is added to a strong acid. What colour does it turn?
Dark red
Universal indicator is added to a mild acid. What colour does it turn?
Orange
Universal indicator is added to a weak acid. What colour does it turn?
Yellow
Universal indicator is added to a neutral substance. What colour does it turn?
Green
Universal indicator is added to a weak alkali. What colour does it turn?
Dark blue
Universal indicator is added to a mild acid. What colour does it turn?
Blue/purple
Universal indicator is added to a weak alkali. What colour does it turn?
Purple/pink
What are the four indicators?
Universal Indicator, litmus, methyl orange, phenolphthalein
What colour does litmus turn in acidic, neutral and alkaline solutions?
Acidic=red
Neutral=purple
Alkaline=blue
What colour does methyl orange turn in acidic, neutral and alkaline solutions?
Acidic =red
Neutral = yellow
Alkaline = yellow
What colour does phenolphthalein turn in acidic, neutral and alkaline solutions?
Acidic = colourless Neutral = colourless Alkaline = pink
What is the reaction between an acid and base called? What does it produce?
Neutralisation reaction, salt and water
Acid + base > ?
Salt + water
What can neutralisation reactions in aqueous solutions be shown as?
An ionic equation in terms of H^+ and OH^- ions
H^+(aq) + OH^-(aq) > ?
H(little2)O(l)
At pH 7 what can we say about concentration of hydrogen and hydroxide ions?
Concentration of hydrogen ions is equal to the concentration of hydroxide ions
Give the 6 steps of a practical investigating the neutralisation reaction between calcium oxide (a base) and dilute hydrochloric acid
1) measure set volume of dilute hydrochloric acid into conical flask. Use Pipette or measuring cylinder.
2) measure fixed mass of calcium oxide using mass balance
3) add calcium oxide to hydrochloric acid (could also be done with calcium hydroxide)
4) wait until base completely reacts, record pH of solution, using pH probe or Universal indicator paper.
5) repeat steps 2+3 until all acid has reacted. This is when unreacted calcium oxide sits at bottom of flask
6) plot graph to show how pH changes with the mass of base added.
What would you expect the graph (showing pH changes with the base of mass added) ((using results from a practical investigating the neutralisation reaction between calcium oxide (a base) and dilute hydrochloric acid)) to look like?
Y axis is pH, x axis is amount of base added. When you first start adding base, pH changes slowly. Sudden change as you approach point where the solution is neutral.
What do acids do when they make contact with solution? What does this mean?
Hey can ionise (dissociate) in solution. They split up to produce a hydrogen ion, H^-, and another ion
HCl in water makes what?
H^+ + Cl^-
HNO(little3) in water makes what?
H^+ + NO(little3)^-
Give three examples of strong acids
Sulfuric, hydrochloric and nitric acids
WHat can we say about how strong acids ionise in water, what does this mean and what kind of pH do the tend to have?
Strong acids ionise almost completely in water. Large proportion of the acid molecules dissociate to release H^+ ions, they tend to have low pHs (pH 0-2)
WHat can we say about how weak acids ionise in solution, what does this mean and what kind of pH do the tend to have?
Weak acids do not fully ionise in solution. only a small proportion of the acid molecules dissociate to release H^+ ions. Their pHs tend to be around 2-6
Is the ionisation of weak acids being reversible or irreversible, and what does this mean for the equilibrium? Why?
Ionisation of weak acid is a reversible reaction, which sets up an equilibrium. since only a few of the acid particles release H^+ ions, the equilibrium lies well to the left.
Give an example equation to show the dissociation of weak acid in solution, using CH(little3)COOH
CH(little3)COOH (top half arrow pointing right and bottom half arrow pointing left to show partial dissociation) H^+ + CH(little3)COO^-
What does acid strength tell you
What proportion of the acid molecules ionise in water
What does concentration of acid measure?
How much acid there is in a litre (1dm^3) of water. Basically, how watered down the acid is
When is an acid said to be concentrated?
When it has a large number of acid molecules compared to the volume of water
When is an acid said to be dilute?
When it has a small number of acid molecules compared to the volume of water
What is concentration used to describe? (The actual thing it’s describing, not what it means)
The total number of dissolved acid molecules
How does number of grams (or moles) of acid per dm^3 relate to concentration of the acid
The more grams of acid per dm^3, the more concentrated the acid is
If the concentration of H^+ ions in an acid increases by a factor of 10, what happens to the pH?
It decrease by 1
If the concentration of H^+ ions in an acid increases by a factor of 100, what happens to the pH?
100 (=10x10), pH decreases by 2 (=1+1)
If the concentration of H^+ ions in an acid decreases by a factor of 10, what happens to the pH?
Increases by pH of 1
A solution with a hydrogen ion concentration of 0.001mol/dm^3 has a pH of 4. What would happen to the pH if you increase the hydrogen ion concentration to 0.01mol/dm^3?
The H^+ concentration has increased by a factor of 10, so the pH would decrease by 1. So the new pH would be 4-1 = 3
What kind of compound is a salt?
An ionic compound
In general, what kind of salt does Hydrochloric acid Sulfuric acid Nitric acid Produce?
Hydrochloric acid = chloride salts
Sulfuric acid = sulphate salts
Nitric acids = nitrate salts
Acid + metal oxide > ?
Salt + water
2HCl + CuO > ?
CuCl(little2)+ H(little2)O
CuCl(little2) = copper chloride
H(little2)SO(little4) + ZnO > ?
ZnSO(little4) + H(little2)O
ZnSO(little4) = zinc Sulfate
2HNO(little3) + MgO > ?
Mg(NO(little3))(little2) + 2H(little2)O
Mg(NO(little3))(little2)=magnesium nitrate
Acid + metal hydroxide > ?
Salt + water
HCl + NaOH > ?
NaCl + H(little2)O
NaCl = sodium chloride
H(little2)SO(little4) + Zn(OH)(little2) > ?
ZnSO(little4) + 2H(little2)O
ZnSO(little4) = zinc Sulfate
HNO(little3) + KOH > ?
KNO(little3) + H(little2)O
KNO(little3) = Potassium Nitrate
When acids react with metals or metal carbonates, what forms?
Salts
Acid + metal > ?
Salt + hydrogen
2HCl + Mg > ?
MgCl(little2) + H(little2)
MgCl(little2) = magnesium chloride
H(little2)SO(little4) + Mg > ?
MgSO(little4) + H(little2)
MgSO(little4) = magnesium Sulfate
What happens when you react nitric acid with metals?
You get a nitrate salt, but instead of hydrogen gas the other products are usually a mixture of water, NO and NO(little2)
How do you test for hydrogen? Why does this work?
Put a lit splint into a test tube with supposed hydrogen in it. It will make a squeaky pop if there’s hydrogen.
The noise comes from the hydrogen burning with the oxygen in the air to form water
Acid + metal carbonate > ?
Salt + water + carbon dioxide
2HCl + Na(little2)CO(little3) > ?
2NaCl + H(little2)O + CO(little2)
2NaCl = sodium chloride
H(little2)SO(little4) + K(little2)CO(little3) > ?
K(little2)SO(little4) + H(little2)O + CO(little2)
K(little2)SO(little4) = potassium Sulfate
2HNO(little 3) + ZnCO(little3) > ?
Zn(NO(little3))(little2)+H(little2)O+CO(little2)
Zn(NO(little3))(little2) = zinc nitrate
How do we test for carbon dioxide?
Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn cloudy
Two solutions are mixed. A salt forms as a precipitate. What does this mean for the salt?
It’s an insoluble salt
Two solutions are mixed. A salt forms in solution. What does this mean for the salt?
It’s soluble.
Common salts or sodium, potassium and ammonium. Soluble or insoluble?
Soluble
Nitrates. Soluble or insoluble?
Soluble
Common chlorides. Soluble or insoluble?
Soluble. (Except silver chloride and lead chloride)
Common Sulfates. Soluble or insoluble?
Soluble, except lead, barium and calcium Sulfate
Common carbonates and hydroxides. Soluble or insoluble?
Insoluble, except sodium, potassium and ammonium ones
How do you make a pure, dry sample of an insoluble salt?
You can use a precipitation reaction. Pick the two right salts and react them together to make an insoluble salt.
How do you make lead chloride? (Insoluble)
Mix lead nitrate and sodium chloride (both soluble)
Leave nitrate + sodium chloride > ?
Lead chloride + sodium nitrate
Pb(NO(little3))(little2)(aq) + 2NaCl(aq) > ?
PbCl(little2)(S)+2NaNO(little3)(aq)
Give Seven steps of a precipitation reaction, for lead nitrate + sodium chloride > lead chloride + sodium nitrate
1) add 1 spatula of lead nitrate to test tube. Add deionised water to dissolve it. Shake thoroughly so lead nitrate is all dissolved. I’m separate test tube, do same with 1 spatula sodium chloride
2) tip the 2 solutions into small beaker, stir. Lead chloride should precipitate out.
3) put folded filter paper in filter funnel, stick funnel in conical flask.
4) pour contents of beaker into filter paper
5) swill our beaker with more water, tip this into filter. Get all precipitates from beaker.
6) rinse filter with deionised water so all soluble sodium nitrate is washed away
7) scrape the lead chloride onto fresh filter paper, leave to dry
Give the five steps of making soluble salts using an acid and an insoluble base
1) make soluble salt by reacting acid that contains one of the ions you want in the salt with an insoluble base that contains the other ion you need (often a metal oxide or metal hydroxide)
2) heat up the acid in a water bath, speeding up reaction between acid and insoluble base. Do this in fume cupboard to contain gases.
3) add base (in excess) to acid. Base and acid will react and produce soluble salt and water. Excess solid should sink to bottom.
4) filter off excess solid to get a solution containing only salt and water
5) heat solution gently, using Bunsen, to evaporate off some ware.r leave to cool and salt will crystallise. Filter off solid salt and leave to dry.
How do you make an insoluble salt?
Acid/(alkali or base) reactions. You make a soluble salt by reacting an acid that contains one of the ions you want in the salt with an insoluble base that contains the other ion you need (often a metal oxide or metal hydroxide). For some salts, you use metal instead of a base.
You can add copper oxide to warm sulfuric acid to make a solution of copper Sulfate:
CuO(s) + H(little2)SO(little4)(aq) > CuSO(little4)(aq)+ H(little2)O(l)
What happens when you evaporate off water and leave the solution?
It will crystallise, you should get blue crystals of hydrated copper Sulfate, which can be filtered off and dried
What’s the issue with reacting an acid with an alkali instead of a base to make a soluble salt?
You can’t tell when the reaction has finished, there’s no signal that all the acid has been neutralised. You also can’t add alkali in excess, it will contaminate the soluble salt.
In making soluble salt using an acid/alkali reaction, what do we need to do to get the exact amount of acid?
Do a titration
Give the five steps of creating soluble salts using an acid/alkali reaction
1) measure set amount of acid into conical flask using a Pipette. Add a few drops of indicator - methyl orange
2) slowly add alkali to acid, using a burette, until you reach the end point - this is when acids been exactly neutralised, indicator changes colour
3) Carry out the reaction using the same columns of alkali and acid, with no indicator, so salt won’t be contaminated with indicator
4) solution that remains when reaction is complete contains only salt and water
5) evaporate off some water and leave solution to crystallise. Filter off solid and dry it.
