Get premium membership and access questions with answers, video lessons as well as revision papers.
Elements:
An element is a substance that cannot be broken down into other substances through
chemical means
An element is a chemical substance that can’t be divided or changed into other chemical
substances by any ordinary chemical means. The smallest unit of an element is the atom.
There are 109 known elements. Most of these are natural, but some are man-made. The
elements we know are represented in the Periodic Table of the Elements, where each element
is abbreviated to a chemical symbol. Examples of elements are magnesium (Mg), hydrogen (H),
oxygen (O) and carbon (C).
Compound:
A substance made up of two or more elements that are joined together in a fixed ratio.
A compound is a chemical substance that forms when two or more elements combine in a fixed
ratio. Water (H2O), for example, is a compound that is made up of two hydrogen atoms for
every one oxygen atom. Sodium chloride (NaCl) is a compound made up of one sodium atom
for every chlorine atom. An important characteristic of a compound is that it has a chemical
formula, which describes the ratio in which the atoms of each element in the compound occur.
vindori answered the question on September 23, 2019 at 11:34
- Calculate the number of Calcium atoms in 10g of calcium.
(Ca = 40, Avogadro number = 6.0 x 1023)(Solved)
Calculate the number of Calcium atoms in 10g of calcium.
(Ca = 40, Avogadro number = 6.0 x 1023)
Date posted: September 23, 2019. Answers (1)
- Your friend’s clothes have caught fire. In order to extinguish the fire you decide to cover with a damp blanket. (Solved)
Your friend’s clothes have caught fire. In order to extinguish the fire you decide to cover with a damp blanket. What is the purpose of the damp blanket?
Date posted: September 23, 2019. Answers (1)
- The flow chart below shows a series of reactions starting withpropan-l-ol. Study it and answer the questions that follow.(Solved)
The flow chart below shows a series of reactions starting withpropan-l-ol. Study it and answer the questions that follow.
(i) Name:
I. Process Y
II. Substances R and C
III. Process W
IV. Polymer X
(ii) Write a balanced chemical equation for the combustion of propane.
(iii) State one use of polymer X
Date posted: September 23, 2019. Answers (1)
- State how burning can be used to distinguish between prepane and propyne. Explain your answer.(Solved)
(a) State how burning can be used to distinguish between prepane and propyne. Explain your answer.
(b) Draw the structural formular of the 4th member of the homologous series in which propyne is a member
Date posted: September 23, 2019. Answers (1)
- Biogas is made from natural organic waste. A from four student set –up the apparatus below to investigate the composition of the gas. He passed...(Solved)
Biogas is made from natural organic waste. A from four student set –up the apparatus below to investigate the composition of the gas. He passed it over heated copper (II) oxide. After that he obtained two products. One was cooled in a boiling tube while the other was collected using a syringe.
(a) What is the function of calcium oxide
(b) Name product
i) P
ii) Y
(c) Give the two observations made in tube X
(d) i) Name the type of reaction taking place in tube X
ii) Write the equation for the reaction above in (d)(i)
(e) What elements are present in biogas
(f) Explain why one tube in boiling tube Q is longer than the other
Date posted: September 23, 2019. Answers (1)
- Using the following thermochemical equations draw an energy cycle diagram.(Solved)
Using the following thermochemical equations draw an energy cycle diagram.
(i) Name the heat of change represented by thermochemical equation A
(ii) Using thermochemical equations A, B, C. Calculate the molar heat of combustion of ethyne
(iii) Give 3 factors considered for choosing a good fuel
Date posted: September 23, 2019. Answers (1)
- The following are half-cell reactions and their reduction potentials
(i) Write the cell representation for the electrochemical cell that would give the highest E? value.
(ii)...(Solved)
The following are half-cell reactions and their reduction potentials
(i) Write the cell representation for the electrochemical cell that would give the highest Eθ value.
(ii) Give one industrial use of electrolysis
Date posted: September 23, 2019. Answers (1)
- Study the diagrams below.(Solved)
Study the diagrams below.
(a) State the observations made at I and II
(b) Write the equation to show the reactions at II if dry sulphur (IV) oxide was used in place of dry chlorine.
Date posted: September 20, 2019. Answers (1)
- Study the flow chart below and answer the questions that follow(Solved)
Study the flow chart below and answer the questions that follow
Process Y
i. Write the formula of Alcohol X, Compound Z and name process Y.
ii. Propane and Chlorine react as shown below :
a) Name the type of reaction that takes place.
b) State the condition under which this reaction takes place.
Date posted: September 20, 2019. Answers (1)
- Study the table below and answer the questions that follow(Solved)
Study the table below and answer the questions that follow
i) What name is given to a series of organic compounds like the ones in the table?
ii) To what class of organic compounds does the above hydrocarbon belongs?
iii) Select one hydrocarbon that would be a gas at room temperature (298K) given a reason for your answer.
iv) Give the formula of the seventh member of the above series.
v) What is the relationship between the boiling point and the relative molecular masses of the hydrocarbons in the table above?
Explain your answer.
Date posted: September 20, 2019. Answers (1)
- Study the scheme below and answer questions that follow.(Solved)
Study the scheme below and answer questions that follow.
i) Name
Gas K
Gas M
ii) State observation made in
Step I
Step II
iii) State the conditions necessary for step II to occur.
iv) Write an equation to show how pollution effect of sulphur (IV) oxide is controlled in contact process.
v) Explain the role of sulphur in vulcanization of rubber.
Date posted: September 20, 2019. Answers (1)
- Study the structure below and answer questions that follow.(Solved)
Study the structure below and answer questions that follow:
a) What observation is made when the molecule above is heated to a temperature of 1130 C
b) Write an equation for the reaction of atom of the above structure with hydrogen.
Date posted: September 20, 2019. Answers (1)
- Equal masses of magnesium ribbon were reacted separately with equal volumes of 1M hydrochloric acid and 1M methanoic acid. The results were plotted on a...(Solved)
Equal masses of magnesium ribbon were reacted separately with equal volumes of 1M hydrochloric acid and 1M methanoic acid. The results were plotted on a graph as shown below. Two curves X and Y were obtained.
a) Explain which curves represents:
i) 1M hydrochloric acid.
ii) 1M Methanoic acid.
b) State the significance of point Z.
c) Write ionic equation for the reaction between magnesium and dilute hydrochloric acid.
d) Calculate the maximum mass of the gas that would be liberated if 1.2g of magnesium reacted with excess hydrochloric acid.
(Mg = 24, H =1).
e) Calculate the volume of the gas produced in (e) above at r.t.p (molar gas volume at r.t.p) = 24dm3.
Date posted: September 20, 2019. Answers (1)
- The arrangements below shows a set-up to investigate the effect of an electric current on molten lead (II) iodide.(Solved)
The arrangements below shows a set-up to investigate the effect of an electric current on molten lead (II) iodide.
a) Identify two mistakes in the set-up.
b) State three observations made after correcting the mistakes.
c) What particles are responsible for electrical conductivity?
d) Write the equations for the reactions taking place at the electrodes.
e) Indicate on the diagram direction of flow of electric current.
Date posted: September 20, 2019. Answers (1)
- Study the information in the table below and answer the questions that follow, letters do not represent actual symbols of the element.(Solved)
Study the information in the table below and answer the questions that follow, letters do not represent actual symbols of the element.
a) Write the electronic configuration of an ion of elements T and U.
b) Why do the elements represented by R and S have two values of melting point.
c) Select an element:
i) Which is the most electronegative.
ii) That belongs to period 4, explain.
d) Explain why:
i) Ionic radius of R is bigger than its atomic radius.
ii) The atomic radius of L is bigger than that of R yet they are in the same period.
e) Using dots (.) and cross (x) to represent outermost electron show bonding in the compound formed between L and M.
f) Write an equation for the reaction that occurs between U and water.
g) Describe how a solid mixture of the sulphate of element N and lead (II) sulphate can be separated into solid sample of dry lead (II) sulphate.
Date posted: September 20, 2019. Answers (1)
- Study the set-up of apparatus below and answer the questions that follow.(Solved)
Study the set-up of apparatus below and answer the questions that follow.
a) State and explain the observation that would be made in tube L as the experiment progresses in the first few minutes.
Observation.
Explanation.
b) How would the observations in the tube L change if the experiment is carried out for a long time. Explain using a chemical equation.
Observation.
Equation.
c) State three observations made when liquid S is reacted with sodium metal.
d) State the use of the suction pump in this experiment.
Date posted: September 19, 2019. Answers (1)
- Study the chart below and answer the questions that follow.(Solved)
Study the chart below and answer the questions that follow.
(a) Name:
(i) Cations present in mixture X.
(ii) Anions present in the solution.
(b) Write an equation to show how the white precipitate in step III is formed.
Date posted: September 19, 2019. Answers (1)
- When solid Zinc carbonate was added to a solution of hydrogen chloride in methylbenzene, there was no observable change.On addition of some water to the...(Solved)
When solid Zinc carbonate was added to a solution of hydrogen chloride in methylbenzene, there was no observable change.On addition of some water to the mixture there was effervescence. Explain these observations.
Date posted: September 19, 2019. Answers (1)
- Graphite is an allotrope of carbon. Distinguish between allotropes and isotopes.(Solved)
Graphite is an allotrope of carbon. Distinguish between allotropes and isotopes.
Date posted: September 19, 2019. Answers (1)
- Graphite is a non- metal most commonly used as an electrode. State two properties that makes it suitable for use as an electrode.(Solved)
Graphite is a non- metal most commonly used as an electrode. State two properties that makes it suitable for use as an electrode.
Date posted: September 19, 2019. Answers (1)