Chemistry expo

CHEMISTRY ANSWERS

1ai) acid-base indicator is a substance that indicates the degree of acidity or basicity of a solution through characteristic color changes.

1aii) Litmus paper

2ai) 1 The Periodic Law states that the physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number.

*DEFINE THE TERM MOLE*
e) A mole of a substance is the amount containing as many elementary entities as the number of atoms in exactly 12 grams of carbon-12.
1ai) acid-base indicator is a substance that indicates the degree of acidity or basicity of a solution through characteristic color changes.

1aii) Litmus paper

2ai) 1 The Periodic Law states that the physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number.
THEORY
1ai)
an acid base indicator is a weak acid or weak base that exhibits a colour change as the concentration of hydrogen (H^+) or hydroxide (H^-) ions changes in an aqueous solution
1aii)
methyl-orange
1b)
i)oxidizing agent
ii)mixed anhydride
1c)
enthalpy of combustion is the heat evolved when one mole of a substance is completely burns in oxygen gas under standard conditions
1cii)
enthapy of combustion is always negetive since it involvs a rise in temperature and heat of reactants is greater than the heat of products
1d)
primary cell is a cell that cannot be re charged while secondary cell is a cell that can be recharged

5c(I) Similarities between nuclear reaction and chimical reaction:
Both result to formation of new substances
Both release heat energy

5c(ii) Uses of radioactive nuclides (pick 2)
Medical Uses: intense gamma radiation can be used in the treatment of cancer. Eg iodine-131 and phosporous-32 are used in treating cancer of the thyroid gland and leukemia respectively
Sterilization: Objects are irradiated with gamma radiations to kill germs leaving it sterile. This is used in sterilizing surgical equipment and other medical apparatus.
Agricultural purposes: radioactive radiation is employed in agricultural research to induce mutations in plants and animals to obtain new and improved varieties with desirable characteristics. It is also used in insect and pest control.
Industrial uses: beta and gamma radiations are used for monitoring, measuring and controlling the thickness of materials such as paper, plastic and metal during production by dictating the variations in intensity of radiations passing through it

2aii) Electron affinity
Ionization energy
Electronegativity
2ai)ii The periodic table arranges the elementsby periodic properties, which are recurring trends in physical and chemicalcharacteristics. ... These trends explainthe periodicity observed in the elementalproperties of atomic radius, ionization energy, electron affinity, and electronegativity.

CHEMISTRY ANSWERS

1ai) acid-base indicator is a substance that indicates the degree of acidity or basicity of a solution through characteristic color changes.

1aii) Litmus paper

2ai) 1 The Periodic Law states that the physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number.

*DEFINE THE TERM MOLE*
e) A mole of a substance is the amount containing as many elementary entities as the number of atoms in exactly 12 grams of carbon-12.