Chemistry Past Questions And Answers
Hardness of water is caused by the presence of ions of
- A. magnesium and silver
- B. cacium and magnesium
- C. sodium and potassium
- D. calcium and sodium
If the change in free energy of a system is -899 Jmol-1 and the entropy change is 10Jmol-1k-1 at 250C, calculate the enthalpy change.
- A) +2081 J/mol
- B) -2081 J/mol
- C) -649 J/mol
- D) +649 J/mol
The number of electrons in the valence shell of an element of atomic number 14 is?
- A) 1
- B) 2
- C) 3
- D) 4
One of the products of combustion of pentane in excess air is
- A. pentanol
- B. pentene
- C. nitrogen (ll) oxide
- D. carbon (IV) oxide
An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. What is the empirical formula of the compound? [ H = 1.0. C = 12.0, O = 16.0 ]
- A. C3H8O
- B. C6H12O
- C. C6H12O2
- D. C12H12O11
Which of the following equimolar solutions would have the highest conductivity?
- A. NH4NO3(aq)
- B. NaNO3(aq)
- C. Mg(NO3)2(aq)
- D. AI(NO3)3(aq)
An organic compound which decolorizes bromine water is likely to be?
- A. C3H8
- B. C2H6
- C. C4H10
- D. C2H4
A sample of an organic compound was weighed to 0.250g and subjected to Kjeldahl treatment. The ammonia produced was neutralized by 27.0cm3 of 0.100 mol dm?3 HCI. What is the percentage of nitrogen in the compound? [H = 1; N = 14]
- A) 18.4%
- B) 17.8%
- C) 15.1%
- D) 13.3%
Which one of the following is not a mixture?
- A. Air
- B. Mercury
- C. Milk
- D. Cement
The knowledge of half-life can be used to
- A. create an element
- B. detect an element
- C. split an element
- D. irradiate an element