CHEMISTRY PAPER 1 - KCSE 2019 MARANDA MOCK EXAMINATION

Elements Q, S, T, U, R and P belong to the same period in the periodic table. The ions formed by the atoms of the elements are given below:
Q²⁺, U^-,T ²⁺,R³⁺,P⁺and S^3-
1. Arrange the elements in order of increasing atomic size. [2mks]
2. Suggest a reason why elements P and Q cannot react with each other to form a compound.[1mk]

The diagram below represents a set-up that can be used to prepare and collect oxygen gas.
1. Name solid P. [1mk]
2. What property of oxygen makes it possible for its collection as indicated by the diagram.[1mk]
3. Explain why it is important not to collect any gas for the first few seconds of the experiment.[1mk]

M grammes of a radioactive isotope decayed to 5 grammes in 100 days. The half-life of the isotopes is 25 days.
1. What is meant by the term half-life? [1mk]
2. Calculate the initial mass of M of the radioactive isotope. [2mks]

Dilute hydrochloric acid is warmed with sodium sulphide
1. Write an equation for the reaction involved. [1mk]
2. State a chemical test for the gas evolved. [1mk]

The system below is at equilibrium.
N_2[g]+O_2[g] ⇋ 2NO_[g] H=+94KJ
Explain how an increase in the following affects the equilibrium position. [3mks]
1. Temperature
2. Pressure
When a current of 2.5 amperes was passed through a cell containing T²⁺ ions of a metal for 25 minutes, the mass of the cathode increased by 0.36g.Determine the relative atomic mass of element T.(IF=96500C). [3mks]

Describe how you would prepare crystals of sodium nitrate starting with 200cm³ of 2m sodium hydroxide. [3mks]
1. Name the polymer with the following structural formula.
  -CH-CH₂-CH-CH₂-CH-CH₂CH-CH₂-
  Cl Cl Cl Cl
2. State one commercial use of the polymer. [1mk]

In one of the dry practical assignment to analyse cat ion in a salt, the following observations were made.

TEST	OBSERVATIONS	INFERENCES
[i]NaoH drop wise till in excess	White precipitate formed soluble in excess
[ii]NH3 solution drop wise till in excess		Presence of Zn 2+confirmed.

Fill in the blanks in the table above. [2mks]
Give an ionic equation for the reaction that occurs in test (ii) when excess ammonia solution is added. [1mk]

When an electric current was passed through molten substances P and Q in different containers, the observations below were made;
Molten P-Conduct electricity and is not decomposed.
Molten Q-Conducts electric current and a gas is formed at one of the electrodes
Suggest the type of bonding present in;
1. Substance P [1mk]
2. Substance Q [1mk]
1. Stat Gay-Cossack’s law. [1mk]
2. 40cm³of carbon (II) oxide and 40cm³ of oxygen were sparked in a closed vessel.
  1. Write a chemical equation for the reaction that occurs. [1mk]
  2. Determine the composition of the residual gases. [2mks]

The scheme below was used to prepare a cleansing agent. Study it and answer the questions that follow.
1. Give the type of cleansing agent prepared by the above method. [1mk]
2. Name the chemical substance added in step ii. [1mk]
3. What is the purpose of adding the chemical substance named in [ii] above? [1mk]

During the extraction of lead from its ore, one of the main ore used is Galena as shown.
1. Write an equation for the reaction in roasting furnace. [1mk]
2. Name gas P. [1mk]
3. State any two uses of lead metal. [1mk]

The figure below shows the electrolysis of dilute sulphuric (VI) acid.
1. On the diagram label the cathode and the anode. [1mk]
2. Name the gases U and V. [1mk]
3. Write the half cell equation for the reaction taking place at the anode. [1mk]

The chemical equations below are the main reactions in large scale manufacture of sodium carbonate.
NH_{3 (g)}+CO_2[g] +H₂O _[l] → NH₄HCO_3[aq]NH₄HCO_3[aq]+Nacl_[aq] → NaHCO₃+NH₄Cl _[aq]
1. Explain how the two products,NaHCO₃and NH₄Cl are separated. [1mk]
2. How sodium carbonate is finally obtained? [1mk]
3. State two uses of sodium carbonate. [1mk]
20cm³ of an unknown gas Q takes 12.6 seconds to pass through small orifice-10cm³ of oxygen gas takes 11.2 seconds to diffuse through the same orifice under the same conditions of temperature and pressure. Calculate the molecular mass of unknown gas Q. [3mks]
1. Define the term isomerism. [1mk]
2. Draw and name two positional isomers of butene. [2mks]
3. Filter papers dipped in acidified potassium manganate (vii] were placed in two separate gas jars A and B containing pentane and pent-i-ene respectively. Explain what was observed in each case.[2mks]

Piecesof blue and red litmus papers were placed in a beaker containing water into which aluminium chloride had been dissolved.
1. Is dissolving of aluminium chloride in water a physical or a chemical process? Explain. [2mks]
2. State the observations made on the papers. Explain your answer. [2mks]
A mass of 2.5g of acid Hx was dissolved in water and the resulting solution was diluted to a total of 250cm³.15cm³ of the final solution was diluted to a total of 250cm³.15cm³ of the final solution was required to neutralise 25.0cm3 of 0.1m aqueous potassium hydroxide. Calculate the relative molecular mass of the acid. [3mks]
75g of a saturated solution contains 3g of a certain salt. Calculate:
1. The solubility of the salt. [2mks]
2. The percentage of the salt in the saturated solution. [1mk]

Using an energy cycle diagram, calculate the enthalpy change of formation of carbon disulphide.[3mks]
S_[s]+o_2[g] → so_2[g] H=-294 KJmol^-1Cs_2[s]+3o_2[g] → co_2[g]+2so_2[g] H=-1072KJMOL^-1C_[s]+o_2[g] → co_2[g] H=-393KJmol^-1