KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
50kg of ammonium sulphate (NH4)2SO4and 30kg of urea CO(NH2)2 fertilizers were applied in two equal sizes of plots A and B to enrich their nitrogen content.Show by working, which plot was more enriched with nitrogen. (N =14;S = 32; O = 16; C = 12; H = 1)
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Under certain conditions, chlorine gas reacts with sodium hydroxide to form sodium hypochlorite.
(a) Name the conditions under which sodium hydroxide reacts with chlorine to form sodium hypochlorite. (b) State two uses of sodium hypochlorite.
ANSWERS
(a) Cold and dilute sodium hydroxide.
(b) Used in sterilizing of water. Used as a bleaching agent.
The set up below was used to prepare a gas and study some of its properties. Study it and answer the questions that follow:
(a) State and explain the observations made in the:
(i) tube labelled A; (ii) beaker labelled B. (b) State one precaution that should be taken when carrying out this experiment.
ANSWERS
(a) (i) Black solid is deposited.
(ii) The indicator turns red. (b) The experiment should be done in fume chamber or in open air.
Exhaust fumes of some cars contain carbon(II)oxide and other gases.
(a) Explain how carbon (II) oxide is formed in the internal combustion engines. (b) Name two gases other than carbon (II) oxide that are contained in exhaust fumes and are pollutants.
ANSWERS
(a) Carbon (II) oxide is formed in the internal combustion engines when fuel burns under limited oxygen.
(b) Pollutant gas - Carbon (IV) oxide, Nitrogen (1V) oxide and Sulphur (IV) oxide.
During a class experiment, chlorine gas was bubbled into a solution of potassium iodide.
(a) State the observations made. (b) Using an ionic equation, explain why the reaction is redox .
When lead(II) nitrate is heated, one of the products is a brown gas.
(a) Write the equation of the reaction that occurs . (b) If 0.290dm3 of the brown gas was produced, calculate the mass of the lead(II) nitrate that was heated. (R .F.M of lead (II) nitrate = 331; Molar gas volume = 24dm3 ).
A certain mass of gas occupies 0.15dm3 at 293K and 98,648.5Pa. Calculate its Volume at 101,325Pa and 273K.
The set up below shows how nitrogen gas is prepared in a laboratory.
(a) Describe how nitrogen gas us formed in the flask.
(b). Nitrogen is inert, state one use of the gas based on this property.
ANSWERS
(a) Oxygen is used up
(b) Lighting of bulbs
a) A student set up the apparatus as shown in the diagram below to prepare and collect dry ammonia gas.
i) Identify two mistakes in the set up and give a reason for each mistake.
I. Mistake Reason II. Mistake Reason ii) Name a suitable drying agent for ammonia iii) Write an equation for the reaction that occurred when a mixture of ammonium chloride and calcium hydrogen was heated. iv) Describe one chemical test for ammonia gas d) Ammonia gas is used to manufacture nitric (V) acid, as shown below.
i) This process require the use of a catalyst. In which unit is the catalyst used
ii) Identify compound A and B A B iii) Using oxidation number, explain why the conversion of ammonia to nitric(V) acid is called catalytic oxidation of ammonia iv) Ammonia and nitric(V) acid are used in the manufacture of ammonium nitrate fertilizer. Calculate the amount of nitric (V) acid required to manufacture 1000kg ammonium nitrate using excess ammonia.(N=14.0, H=1.0, O=16.0)
The set up below was used to investigate some properties of two gases M and N
The set up below was used to investigate some properties of two gases M and N
When beaker A was filed with gas M, the level of water in the glass tube rose to
point II. When the experiment was repeated using gas N, the level of water dropped to point III. Explain these observations.
Use the information in the table below to answer the questions that follow. The letters do not represent that actual symbols of the elements.
a) Give the reasons why the meling point of:
i) S is higher than that of R ii) V is lower than that of U b) How does the reactivity of W with chlorine compare with that of R with chlorine? Explain, c) Write an equation for the reaction between T and excess oxygen
d) When 1.15g of R were reacted with water, 600cm3 of gass was produced.
Determine the relative atomic mass of R. (Molar gas volume = 24000cm3) e) Give one use of element V
ANSWERS
(a)(i) Metallic bonds in S are stronger than in R.
(ii) V is monoatomic (independent) hence weaker van der waals forces while U is diatomic hence stronger van der waals forces V has less van der waals forces while U has more van der waal forces (b) reacts more vigorously/more reactive/reacts faster - reactivity of group 1 elements increases down the group/Ionisation energy is less than that of R - easier to lose outer electron in W than in R W is more electropositive than R
In an experiment to prepare nitrogen (I) oxide, ammonium nitrate was gently heated in a flask.
a) Write the equation for the reaction that took place in the flask. b) State and explain how the gas was collected. c) A sample of the gas was tested with damp blue and red litmus papers. What observations were made?
The diagram below represents set up for large scale manufacture of hydrochloric acid.
Study it and answer the questions that follow.
a) Name substance X
b) What is the purpose of the glass beads? c) Give two uses of hydrochloric acid.
Analysis of a compound showed that it had the following composition: 69.42% carbon, 4.13% hydrogen and the rest oxygen.
a) Determine the empirical formula of the compound. (C = 12.0, H = 1.0, O = 16.0) b) If the mass of one mole of the compound is 242, determine its molecular formula
Hydrogen sulphide is a highly toxic and flammable gas. It is normally prepared in a fume chamber
.a) Name two reagents that can be used to prepare hydrogen sulphide in the laboratory. b) One of the uses of hydrogen sulphide is to produce sulphur as shown in the following equation; 2H2S(g) + SO2(g) → 3S(s) + 2H2O(l) Identify the reducing agent in this reaction and give a reason for your answer. c) Other than production of sulphuric(IV) acid, state one commercial use of sulphur.
ANSWERS
(a) Iron (II) Sulphide
Hydrochloric acid (b)Reducing agent, hydrogen sulphide The sulphur changes from -2 to zero (c) Vulcanization of rubber Manufacture of sulphur drugs
(a) A few drops of freshly prepared iron (II) sulphate solution were added to potassium nitrate solution in a test – tube. Concentrated sulphuric acid was then carefully added to the mixture. State the observation that were made
(b) Write an equation for the reaction that occurs when solid potassium nitrate is strongly heated
In an attempt to prepare sulphur dioxide gas, dilute sulphuric acid was reacted with barium sulphuric. The yield of sulphur dioxide was found to be negligible explain
The pressure of nitrogen gas contained in a 1dm3 cylinder at -196°C was 107 Pascals.
Calculate the: a) Volume of the gas at 25°C and 105 Pascals. b) Mass of nitrogen gas(Molar volume of gas is 24dm3, N = 14.0)
Aluminium oxide reacts with both acids and bases.
a) Write an equation for the reaction between aluminium oxide and hydrochloric acid. b) Using the equation in (a) above, calculate the number of moles of hydrochloric acid that would react completely with 153.0g of aluminium oxide. (AL = 27.0, 0= 16.0)
Draw the structures and give the name of the three alkaline having molecular formula C5H10
D gm of potassium hydroxide were dissolved in distilled water to make 100cm3 of solution. 50cm3 of the solution- required 50cm3 of 2 M nitric acid for complete neutralization. Calculate the mass D, of potassium hydroxide (KOH)(aq) + HNO3(aq) →KNO3 (aq) + H2O (I) Relative formula mass of KOH = 56
a) Two reagents that can be used to prepare chlorine gas are manganese (IV) oxide and concentrated hydrochloric acid.
i) Write an equation for the reaction. ii) Give the formula of another reagent that can be reacted with concentrated hydrochloric acid to produce chlorine gas. iii) Describe how the chlorine gas could be dried in the laboratory b) In an experiment, dry chlorine gas was reacted with aluminium as shown in figure 1.
i) Name substance A.
ii) Write an equation for the reaction that took place in the combustion tube. iii) 0.84 g of aluminium reacted completely with chlorine gas. Calculate the volume of chlorine gas used (Molar gas volume is 24dm3, Al = 27). iv) Give two reasons why calcium oxide is used in the set up.
Sulphur dioxide and nitrogen dioxide react as shown in the equation below
SO2(g) + NO2(g) → SO3(g) + NO(g)
(i) Using the oxidation numbers of either sulphur or nitrogen, show that this is a redox reaction
(ii) Identify the reducing agent
4.76g of liquid ammonia and 4.76g of liquid nitrogen were each allowed warming up and hanging into gas at warm temperature and pressure. Relative atomic masses: H=1.0 and N=14.0. Using the data given above, explain which gas occupied the greater volume.
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