Elements, Compounds and Mixtures Test - 7

Mixtures are physically combined structures that can be separated into their original components. A chemical substance is composed of one type of atom or molecule. A mixture is composed of different types of atoms or molecules that are not chemically bonded.

Therefore, option (b) is correct.

Petrol, or gasoline, evaporates faster than most liquids because of its weak intermolecular attractions. Petrol is a mixture of hydrocarbons with the main constituent being octane, C8H18. Octane is a non-polar molecule. Some hydrocarbons are more volatile (evaporate more quickly) than petrol.

Therefore, option (b) is correct

Chemical changes occur when bonds are broken and/or formed between molecules or atoms. This means that one substance with a certain set of properties (such as melting point, color, taste, etc.) is turned into a different substance with different properties. One good example of a chemical change is burning a candle.

Therefore, option (b) is correct.

Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table.

Therefore, option (b) is correct.

Evaporating dishes are used to evaporate excess solvents – most commonly water – to produce a concentrated solution or a solid precipitate of the dissolved substance. Most are made of porcelain or borosilicate glass.

Therefore, option (a) is correct.

A suspension is a heterogeneous mixture that separates into layers over time. For example, if you shake up a container of sand and water, the sand mixes with the water and forms a suspension. Over time, the suspended particles of sand settle to the bottom of the container.

Therefore, option (b) is correct.

Elements can be chemically combined into compounds, therefore, a compound consists of two or more elements combined, in definite proportions, by chemical means. Compounds may be formed by combining atoms of their constituent elements by ionic bonds or by covalent bonds.

Therefore, option (b) is correct.

Compound is a pure substance made up of two or more substances combined chemical in a definite (or constant) proportion by mass (or weight). When two or more elements combine together chemically to form a new substance called compound.

melting of butter is a physical change because the butter can be solidified again (i.e. reversible change). In melting of butter only state of the chemical substance is changed.

Therefore, option (A) is correct.

Bronze is an alloy consisting primarily of copper, commonly with about 12%tin and often with the addition of other metals (such as aluminum,manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon.

Therefore, option (a) is correct.

The fossil fuels are coal, oil and natural gas. When fossil fuels are burned, they release nitrogen oxides into the atmosphere, which contribute to the formation of smog and acid rain. Burning of natural gas produces nitrogen oxides and carbon dioxide, but in lower quantities than burning coal or oil. When coal is burned, carbon dioxide, sulfur dioxide, nitrogen oxides and mercury compounds are released. Burning oil at power plants produces nitrogen oxides, sulfur dioxide, carbon dioxide, methane and mercury compounds. Carbon monoxide is released when car engines burn fossil fuels.

Potato strips were soaked in 3, 5 or 7% NaCl solutions (25 °C) previous to frying, to study the effect on oil uptake. Sensory responses indicated the best texture and lowest oil uptake at 3% NaCl solution for 50 min. Soaking had no effect (P<0.05) on color (L∗, a∗ and b∗) or moisture loss during deep fat frying at 180 °C. Soaking significantly reduced oil uptake from 0.13 to 0.10 g oil/g dry matter and increased the measured texture parameters (hardness to penetrate both crusts, and both work and initial rigidity).

Therefore, option (A) is correct.

A pure substance contains only one type of particles which can either be atoms or molecules or elements.

Therefore, option (A) is correct.

The conversion of 20g will be 0.02kg.

Therefore, option (d) is correct.

Saturated Solution: A solution with a solute that dissolves until it is unable to dissolve any more, leaving the undissolved substances at the bottom.

Unsaturated Solution: A solution (with less solute than the saturated solution) that completely dissolves,  in which still more solute can be dissolved.

Supersaturated solution: Solution that is more concentrated than a saturated solution is known as a supersaturated solution. If a crystal of solute is added to this solution, the excess of solute crystallizes.

A dilute solution: is one in which there is a relatively small amount of solute dissolved in the solution.

A concentrated solution: contains a relatively large amount of solute dissolved in the solution.

Hence option A is correct.