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
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(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)
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Date posted: September 23, 2019. Answers (1)
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(i) Name:
I. Process Y
II. Substances R and C
III. Process W
IV. Polymer X
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(iii) State one use of polymer X
Date posted: September 23, 2019. Answers (1)
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Date posted: September 23, 2019. Answers (1)
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(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)
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Date posted: September 23, 2019. Answers (1)
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(iii) Give 3 factors considered for choosing a good fuel
Date posted: September 23, 2019. Answers (1)
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(ii)...(Solved)
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Date posted: September 23, 2019. Answers (1)
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(a) State the observations made at I and II
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Date posted: September 20, 2019. Answers (1)
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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 :
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b) State the condition under which this reaction takes place.
Date posted: September 20, 2019. Answers (1)
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Study the table below and answer the questions that follow
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ii) To what class of organic compounds does the above hydrocarbon belongs?
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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)
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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)
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Study the structure below and answer questions that follow:
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Date posted: September 20, 2019. Answers (1)
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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).
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Date posted: September 20, 2019. Answers (1)
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The arrangements below shows a set-up to investigate the effect of an electric current on molten lead (II) iodide.
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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)
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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.
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Date posted: September 20, 2019. Answers (1)
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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.
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d) State the use of the suction pump in this experiment.
Date posted: September 19, 2019. Answers (1)
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(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)
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Date posted: September 19, 2019. Answers (1)
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Date posted: September 19, 2019. Answers (1)
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Date posted: September 19, 2019. Answers (1)