Question

What type of change-physical or chemical-is necessary to separate the following? [Hint: Refer to a listing of the elements.] (a) sugar from a sand/ sugar mixture (b) iron from iron oxide (rust) (c) pure water from seawater (d) water from a slurry of sand in water

Short answer

(a) Physical change - sugar from a sand/sugar mixture\n(b) Chemical change - iron from iron oxide (rust)\n(c) Physical change - pure water from seawater\n(d) Physical change - water from a slurry of sand in water

Step-by-step solution

Sugar from a sand/sugar mixture

The most effective method for separating a sand and sugar mixture would be through dissolution and filtration. In this process, water is added to the mixture, enabling the sugar to dissolve while the sand does not. Filtration then allows for the separation of the insoluble sand from the sugar solution. As this involves no chemical changes, only physical changes to the mixture, it is considered a physical reaction.

Iron from iron oxide (rust)

A chemical reaction is required to separate iron from iron oxide. This process would typically involve a method such as electrolysis or a reduction reaction. For instance, the application of carbon monoxide to the iron oxide, a method widely referred to as the 'Blast Furnace' method, would yield iron and carbon dioxide. As this involves changes in the composition of the substance, it is a chemical change.

Pure water from seawater

Distillation, a process that involves evaporation and condensation, would most effectively separate pure water from seawater. Seawater is boiled, turning the water to steam and leaving behind solid salt. The steam is then condensed back into liquid water in a new container. Given that no chemical changes occur in this process, it is considered a physical reaction.

Water from a slurry of sand in water

Water from a slurry of sand can be separated through the process of filtration or evaporation. The water filters out, leaving the sand behind, or the slurry is left to evaporate, with the sand remaining as a residue. As there is no change in the chemical composition of the substances, it is a physical change.

Key concepts

Mixture Separation

Mixture separation is a fundamental technique used to separate different substances while maintaining their original components. This approach plays a significant role in identifying, analyzing, and purifying materials in both laboratory and industrial settings. Techniques for mixture separation depend on the properties of the materials involved, such as size, solubility, boiling point, and magnetic properties. Common methods include:

• Dissolution and Filtration for separating soluble substances from insoluble ones.
• Distillation for separating liquids based on their boiling points.
• Magnetic Separation for isolating magnetic materials from non-magnetic ones.
• Centrifugation for separating substances of different densities.

These methods highlight how physical properties can be utilized to isolate and extract desired materials without changing their chemical structures.

Dissolution and Filtration

Dissolution and filtration is a straightforward method used to separate mixtures comprising a soluble and an insoluble substance. Imagine you have a mixture of sand and sugar. To separate these, you would:

• Add water to the mixture. Only the sugar dissolves because sand is insoluble in water.
• Stir the mixture to ensure complete dissolution of the sugar.
• Use filter paper and a funnel to separate the dissolved sugar in the water from the sand. The filter paper lets the sugar solution pass through while retaining the sand particles.
• Once the sand is isolated, the sugar can be retrieved by evaporating the water from the solution.

This method effectively uses the property of solubility and involves non-chemical changes, hence it's a physical method.

Electrolysis and Reduction Reactions

Electrolysis and reduction reactions are chemical processes often utilized to decompose compounds or extract elements from ores. Unlike physical changes, these methods alter the chemical composition of substances. For example, converting iron oxide to iron requires a reduction reaction:

• Electrolysis: This method uses electricity to break chemical bonds, typically used for substances like water to produce hydrogen and oxygen gas.
• Reduction Reaction: In metallurgy, a reducing agent like carbon monoxide is used in a blast furnace to convert iron oxide into iron. The chemical equation can be represented as:\[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \]

These processes involve changing chemical compositions and thus are classified as chemical changes.

Distillation Process

The distillation process is a physical method used to separate components based on differences in their boiling points. It's frequently used for purifying liquids and separating mixtures like seawater:

• The mixture is heated until one component boils and turns into vapor. For seawater, water is vaporized, leaving salt behind.
• The vapor then travels through a condenser, cooling and converting it back to liquid form, which is collected separately.

This process doesn't alter the chemical nature of the substances involved, making it a physical change. Distillation is vital in industries such as petroleum refining, water purification, and chemical laboratories for preparing pure solvents.