1 2 elements compounds and mixtures

An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.

True. Nitrogen is an element.

False. Water is a compound composed of hydrogen and oxygen atoms chemically combined.

A compound is a pure substance made up of two or more different elements chemically combined together.

False. Compounds cannot be separated into their elements by physical means.

A mixture is a combination of two or more substances (elements and/or compounds) that are not chemically combined.

A compound consists of two or more elements that are chemically combined, while a mixture consists of two or more substances that are not chemically combined.

True. All substances can be classified into one of these three types.

The classifications of the following are:

An element consists of only one element, while a compound consists of two or more elements that are chemically combined.

Copper wire is an element.

Copper sulfate is not in the Periodic Table because it is a compound / not an element.

A pure substance consists of only one substance (this can be an element or a compound), while a mixture contains two or more different substances that are not chemically combined.

False. A solution of salt dissolved in water is a mixture.

The melting point is the temperature at which a solid turns into a liquid.

The boiling point is the temperature at which a liquid turns into a gas.

Melting point and boiling point can be used to distinguish a pure substance from a mixture.

False. Pure substances have sharp, specific melting and boiling points, while mixtures have a range of melting and boiling points.

A cooling curve is a graph that shows how a substance changes from a gas to a liquid to a solid as temperature decreases.

A horizontal line on a cooling curve indicates where a substance is changing from a gas to a liquid or from a liquid to a solid.

A pure substance is a single element or compound that contains no other substances.

Pure substances have specific and sharp melting and boiling points, while mixtures have a range of melting and boiling points.

Melting point analysis is used to assess the purity of a substance.

Simple distillation is used to separate:

Simple distillation is a technique used to separate a liquid from a solution (e.g., water from a salt solution) by boiling the solution and condensing the vapour.

Fractional distillation is a technique used to separate two or more liquids that have different boiling points from a mixture.

Filtration separates an undissolved solid from a mixture of solid and liquid.

Crystallisation is used to separate a dissolved solid from a solution.

It is important that the solid (solute) is more soluble in hot solvent than in cold.

Paper chromatography depends upon the solubility of different substances.

Paper chromatography is used to separate substances that have different solubilities in a given solvent, such as identifying the components of a mixture.

The mobile phase in chromatography is the solvent / liquid that travels up the paper.

The baseline (starting line) should be drawn in pencil because it will not contaminate the results / will not run.

False. In paper chromatography, a pure substance only produces one spot.

The technique that separates solutions with more than one type of dissolved solid is chromatography.

A single spot on a chromatogram indicates that the substance is pure.

False. Multiple spots on a chromatogram indicate that the substance is a mixture.

The equation for the retention factor (Rf value) is: Rf =

An Rf value close to 1 indicates that the component is very / highly soluble in the solvent used.

False. The Rf value of a compound depends on the solvent used. If the solvent is changed, the Rf value will change.

The purpose of calculating Rf values is to allow chemists to identify unknown substances.

The Rf values ranges between 0 and 1.

The initial line on a chromatogram should be drawn with a pencil.

There are 3 substances in D.

False. The solvent level should not start above the pencil line, as this would ruin the chromatogram.

The mobile phase is the water, and the stationary phase is the chromatography paper.

True. If two substances are the same, they will produce identical chromatograms.

An Rf value does not have units because it is a ratio.

The black food colouring contains A, E and an unknown.