WS / HW / / RS / 676: 2022 - 2023: TERM: I /II
NAME: _________________________ CLASS: 9 DIV: A B C D E ROLL NO.: ____ DATE: __________
SUBJECT: CHEMISTRY TOPIC: Revision 3 – Answer key TEACHER’S NAME: Mrs. Sneha Mishra
Note: This sheet can be assessed. MARKS / GRADE: __________
_______________________________________________________________________________
1. A compound, X, contains 55.85% carbon, 6.97% hydrogen and 37.18% oxygen.
a. How does this prove that compound X contains only carbon, hydrogen and oxygen?
The total % of carbon , hydrogen and oxygen add up to 100 %.
b. Use the above percentages to calculate the empirical formula of compound X.
X in % 55.85% C 6.97% H 37.18% O
MASS IN 100g 55.85 g 6.97g 37.18g
MOLAR MASS 12 g/mol 1g/mol 16 g/ mol
NO. OF MOLES
4.65 moles = 6.67 moles = 2.32 moles
SIMPLEST RATIO
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c. The Mr of X is 86. What is its molecular formula?
2. Bromine water changes from brown to colourless when added to X.
a. What does this tell you about the structure of X?
X is an unsaturated compound or X has double bond
b. Magnesium powder reacts with an aqueous solution of X. Hydrogen is evolved. What does this
tell you about the structure of X?
X is an acid that releases H+ ions
3. For each of the following, give the name of an element from Period 2 (lithium to
neon), which matches the description. Elements may be used once, more than once
or not at all.
(i) an element which is gaseous at room temperature and pressure
nitrogen / oxygen / fluorine / Neon
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(ii) an element which forms an oxide that is a reactant in photosynthesis
carbon
(iii) an element that is a product of photosynthesis
oxygen
(iv) an element that makes up approximately 78% by volume of the air
nitrogen
(v) an element which has atoms with a full outer shell of electrons
neon
(vi) an element which exists as both diamond and graphite
carbon
(vii) an element that reacts vigorously with cold water
lithium / fluorine
.
(viii) a soft metallic element which is stored in oil
lithium
4. Give the formula of a compound that contains
(i) only boron and oxygen
B2O3
(ii) only lithium and nitrogen
Li3N
5. The first three elements, Na, Mg and Al, are metals. Describe the structure of a typical metal.
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