- What physical properties would you use to separate these mixtures?
a) iron filings and salt b) salt and water - Identify each of the following samples of matter as homogeneous or heterogeneous. Also classify them as an element, compound, or mixture.
a) milk b) glass c) table sugar d) river water e) cough syrup f) nitrogen - What are two ways to distinguish between an element and a compound?
The Correct Answer and Explanation is :
5. What physical properties would you use to separate these mixtures?
a) Iron filings and salt
- Use magnetism to separate the iron filings, as iron is magnetic, while salt is not.
- After separating the iron, dissolve the salt in water, then evaporate the water to retrieve the salt.
b) Salt and water
- Use solubility and boiling point differences:
- Dissolve the salt in water to create a solution.
- Use evaporation or distillation to separate the water from the salt.
6. Identify each sample as homogeneous or heterogeneous and classify as element, compound, or mixture.
a) Milk
- Heterogeneous mixture: Milk is a colloid containing fat globules suspended in water, which makes it non-uniform on a microscopic level.
b) Glass
- Homogeneous mixture: Glass is an amorphous solid made by mixing compounds like silica (SiO₂) and other additives, giving it uniform properties.
c) Table sugar (sucrose)
- Compound: A pure substance with a fixed chemical formula, C₁₂H₂₂O₁₁, made of carbon, hydrogen, and oxygen.
d) River water
- Heterogeneous mixture: Contains water, dissolved minerals, organic matter, and suspended particles, making it non-uniform.
e) Cough syrup
- Homogeneous mixture: A solution with evenly distributed active ingredients and solvents.
f) Nitrogen
- Element: A pure substance consisting of only nitrogen atoms (N₂), with uniform properties.
7. Two ways to distinguish between an element and a compound
- Chemical composition:
- An element consists of only one type of atom (e.g., oxygen, O₂).
- A compound contains two or more elements chemically bonded in fixed ratios (e.g., water, H₂O).
- Decomposition ability:
- An element cannot be broken down into simpler substances by chemical methods.
- A compound can be chemically decomposed into its constituent elements.
Explanation (300 words)
The distinction between elements and compounds lies in their atomic structure and chemical behavior. An element, like nitrogen or gold, is made up of only one type of atom. Its identity is defined by its atomic number, which corresponds to the number of protons in its nucleus. Elements are the building blocks of matter and cannot be simplified chemically. For instance, no chemical reaction can split oxygen (O₂) into anything simpler than oxygen atoms.
Compounds, on the other hand, are formed when two or more elements chemically combine in a fixed proportion. This combination creates entirely new properties. For example, hydrogen (H₂) and oxygen (O₂) are gases under standard conditions, but when chemically bonded as water (H₂O), they form a liquid with distinct characteristics. Compounds can be decomposed into their elements through chemical reactions. For instance, electrolysis of water can separate it into hydrogen and oxygen gases.
Another distinction is in their purity and simplicity. Elements are pure substances, while compounds, though pure in themselves, are more complex due to their combination of elements. Understanding these differences helps in identifying substances and studying their behavior in chemical reactions.