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SPM Seminar 2014 - Chemistry

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the seminar by edunation on 2014

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Form 4 PUSAT TUISYEN KASTURI PREPARED BY:

STRONG ACIDS AND STRONG BASES

The common acids that are almost one hundred percent ionised in water are: HNO3 - nitric acid HCl - hydrochloric acidH2SO4 - sulphuric acid

1. The acids on this short list are called strong acids, because the amount of acid quality of a solution depends upon the concentration of hydrogen ions.

2. Incompletely or partially ionised acids are called weak acids, because there is a smaller concentration of hydrogen ions available in the solution.

3. An example of a weak acid is ethanoic acid.

4. In the list of strong acids, sulphuric acid is the only one that is diprotic, because it has two moles of hydrogen ions per mol of acid

5. The other acids in the list are monoprotic, because it has one mol of hydrogen ions per mol of acid

6. Likewise, there is a short list of strong alkali, ones that completely ionise into hydroxide ions.

7. All of the bases of Group 1 metals are strong bases.

8. Lithium, rubidium and caesium hydroxides are not often used in the lab because they are expensive.

9. Potassium and sodium hydroxides both have the common name of lye.

LiOH - lithium hydroxideNaOH - sodium hydroxideKOH - potassium hydroxide

10. The bases of Group 1 metals are all monobasic. 11. Example of a weak alkali is ammonia.Neutralisation

1. In a neutralization reaction, an acid reacts with a base to form a neutral solution containing a salt and water.

2. When a neutralization is performed in aqueous solution, the essential feature of the reaction is the combination of hydrogen ions and hydroxide ions to form water

HCl (aq) + NaOH (aq) ----> NaCl (aq) + H2O (aq) H+ (aq) + OH- (aq) ----> H2O (l)Concentration of an aqueous

Exercise:

1. What is the molarity of the solution formed by dissolving 49 g of sulphuric acid in 250 cm3 of water? ( H=1, S=32, O=16)

2. What mass of hydrogen chloride is needed to make up 500cm3 of a solution of concentration 4moldm-3 ? (H=1, Cl=35.5)

3. What is the molarity of a sulphuric acid solution, if 15 cm3 of it are neutralised by 20 cm3 of a 0.3 moldm-3 potassium hydroxide solution?

4. 15 cm3 of hydrochloric acid are neutralised by 25 cm3 of 0.06 moldm-3 sodium hydroxide. What is the molarity of the acid?

SPM 2005 (Essay)

(a) The following information is about hydrochloric and ethanoic acid.

1. The pH of 1moldm-3 hydrochloric acid solution is 1

2. The pH of 1moldm-3 ethanoic acid solution is 4

Explain why these two solutions have different pH values [4m]

SPM 2006

(a) 8g of solid sodium hydroxide, NaOH, is dissolved in distilled water to produce a solution of 1000cm3The NaOH solution produced has the concentration of 8gdm-3 and the molarity of 0.2moldm-3(i) State the meaning of the concentration for the solution produced. [1m]

(ii) State the meaning of the molarity for the solution produced. [1m]

(iii) Write the formula that represents the relationship between the number of mole (n), molarity (M), and volume (V) for the solution. [1m]

(iv) Substitute the actual values of the number of mole, molarity and volume of the NaOH solution into the formula in 4(a)(iii)

[Relative molecular mass of NaOH = 40] [1m]

(b) Diagram 4.1 shows the preparation of the standard solution of NaOH 0.2moldm-3(i) What are the two parameters that should be measured accurately to prepare the standard solution of NaOH?

Parameter I:

Parameter II:

[2marks]

(ii) After all the NaOH solution is poured into the volumetric flask, the beaker and the filter funnel must be rinsed several times with distilled water. After each rinse, all of this water is transferred into the volumetric flask.

Give one reason for doing this.

[1 mark]

(iii) What step should be taken to ensure that the meniscus level of the standard solution is exactly in line with the graduation mark on the volumetric flask?

[1 mark]

(iv) A volumetric flask is more suitable to be used in the preparation of the standard solution rather than a beaker.

Why?

[1 mark]

(v) Why is the volumetric flask stoppered after the standard solution is prepared?

[1 mark]

SPM 2005 Question 1SPM 2006 Question 2

Question 3

SPM 2007 Question 5SPM 2008Question 7

Solubility of Salts

Nitrate salts,

NO3-Sulphate salts,

SO42-Chloride salts,

Cl-Carbonate salts,

CO32-

All nitrates are SOLUBLE

All sulphates are SOLUBLE

Except:

BaSO4CaSO4 INSOLUBLEPbSO4

All chlorides are SOLUBLE

Except:

AgCl INSOLUBLE

PbCl2

All carbonates are INSOLUBLE

Except:

Na2CO3K2CO3 SOLUBLE(NH4)2CO3

Salt preparation

There are 2 steps in writing out the preparation of a salt.Step 1: Check solubility of the salt to be preparedStep 2: Check solubility of the parent acid and parent base to be usedThere are 3 main methods available for salt preparation.1)Precipitation reaction

2)Titration

3)Acid neutralisation ( acid +metal, acid + metal oxide, acid + metal carbonate)

Titration

Acid neutralisation

Example 1

Prepare barium(II) sulphate.Step 1: barium(II) sulphate is insolubleConclusion: Use Precipitation methodReagents: soluble barium salt(barium nitrate)+soluble sulphate salt(sodium nitrate)Equation: Ba(NO3)2 (aq) + Na2SO4 (aq) ( BaSO4 (s) + 2NaNO3 (aq)Example 2

Prepare potassium nitrate.Step 1: potassium nitrate is solubleConclusion: Precipitation method impossibleStep 2: potassium hydroxide and nitric acid are solubleConclusion: Titration methodReagents: potassium hydroxide, nitric acidEquation

ExercisesFor the following salts, choose the appropriate method of preparation and describe the preparation with balanced equations and state symbols.a) Ammonium sulphateb) Magnesium nitrate

c) Lead (II) chloride

d) Calcium carbonate

e) Zinc sulphate

f) Copper (II) chloride

g) Potassium sulphate

h) Zinc carbonate

The colours of salts

Identification of anions

Carbonate ion CO32-

Add any dilute strong acid to the suspected carbonate - if colourless gas given off, test with limewater.

Fizzing - colourless gas - turns limewater milky cloudy

Any carbonate + acid ==> salt + water + carbon dioxide,

Example: Magnesium carbonate and nitric acid

All carbonates except sodium and potassium carbonate will decompose when heated to release CO2.

Example: Calcium carbonate heated

Sulphate ions, SO42-To a solution of the suspected sulphate add dilute hydrochloric acid and a few drops of barium chloride or nitrate solution.

A white precipitate of barium sulphate.

Ba2+(aq) + SO42-(aq) ==> BaSO4(s) Any soluble barium salt + any soluble sulphate forms a white dense barium sulphate precipitate.

Chloride ion, Cl-To a solution of the suspected chloride, add dilute nitric acid and silver nitrate solution.

White precipitate of silver chloride forms.

Ag+(aq) + Cl-(aq) ==> AgCl(s)

Nitrate ion, NO3-

Brown ring test Add diluted sulphuric acid, iron(ii) sulphate solution and then concentrated sulphuric acid

Where the liquids meet a brown ring forms.

Identification of cations

Copper(II) ions, Cu2+1. Add a few drops of ammonia (aq) : Blue precipitate which dissolves in excess ammonia to give a deep blue solution

2. Add sodium hydroxide (aq): Blue precipitate which does not dissolves in excess ammonia to give a deep blue solution

Iron (II) ion, Fe2+Add NaOH or NH3, dark green precipitate which is not soluble in excess of NH3 or NaOH

Iron (III) ion, Fe3+Add NaOH or NH3, brown precipitate which is not soluble in excess of NH3 or NaOH

Cation A few drops of NaOHExcess NaOHA few drops of NH3 (aq)Excess NH3 (aq)

Ca2+ White pptWP does not dissolve --------- ---------

Mg2+ White pptWP does not dissolveWhite pptWP does not dissolve

A13+ White pptWP dissolvesWhite pptWP does not dissolve

Zn2+ White pptWP dissolvesWhite pptWP dissolves

Pb2+White pptWP dissolvesWhite pptWP does not dissolve

SPM 2005

Questions:

1. What test could be done to differentiate an aqueous solution of lead(II) nitrate and aluminium nitrate?

2. You are provided with aqueous solutions of sodium carbonate, zinc chloride and sulphuric acid. Explain how zinc sulphate can be prepared.

3.

Which salts could be present in X?

A. zinc carbonate and zinc chloride

B. magnesium carbonate and magnesium nitrate

C. Lead(II)carbonate and lead(II)nitrate

D. Lead(II)sulphate and lead(II)chloride

4.

State the identity of compounds X, Y and Z.

Making a soluble salt

SPM 2010

Question 1

Question 2

Question 4

SPM 2008

Mass of solute (g)

Concentration=

(g/dm3) Volume of solution (dm3)

Amount of moles of solute (mol)

Concentration=

(mol/dm3) Volume of solution (dm3)

[Molarity]

x molar mass

Molarity Concentration

(mol/dm3) (g/dm3)

( molar mass

M1V1=M2V2 MaVa = a

MbVb b

Question 4

Question 6

Soluble

Potassium salts

Sodium salt

Ammonium salts

Soluble

Other soluble salts

Insoluble

Precipitation reaction

ZnO

PbO

FeSO4

FeCl2

Fe(NO3)2

Fe2 (SO4)3

FeCl3

Fe(NO3)3

CuSO4

CuCl2

Cu(NO3)2

CuCO3

CuO

Cu

that occur to

Precipitation

X

Add distilled water

White ppt dissolves

White ppt

Solution

Add

sodium chloride

Heated

Brown acidic gas

Residue Y( brown while hot and yellow when cold)

X

Heated

Add distilled water

White precipitate Z

X solution

Add sodium sulphate solution

Question 3

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