Which of the following substances is a heterogeneous mixture?
A) sodium
B) baking soda
C) dextrose (a sugar) dissolved in water
D) salt and pepper in a glass
The correct answer and explanation is:
The correct answer is:
D) salt and pepper in a glass
Explanation:
To understand why salt and pepper in a glass is a heterogeneous mixture, let’s first define some key terms:
- Substance: A form of matter that has a definite composition and distinct properties. Examples include elements and compounds.
- Mixture: A physical combination of two or more substances where each retains its own chemical identity.
- Homogeneous mixture: A mixture that has a uniform composition throughout, meaning you cannot distinguish its different parts with the naked eye.
- Heterogeneous mixture: A mixture where the components are not uniformly distributed, and you can often see the different parts or phases.
Now, let’s analyze each option:
A) Sodium
Sodium (Na) is a chemical element and a pure substance, not a mixture. It consists of only sodium atoms and has uniform properties throughout.
B) Baking soda
Baking soda is sodium bicarbonate (NaHCO₃), a pure chemical compound, so it’s a substance, not a mixture.
C) Dextrose dissolved in water
Dextrose (a sugar) dissolved in water forms a solution, which is a type of homogeneous mixture. The sugar molecules are evenly dispersed at the molecular level, so the mixture looks uniform throughout.
D) Salt and pepper in a glass
Salt and pepper combined physically form a mixture where the two substances remain distinct. You can see the grains of salt and pepper separately, and they are not uniformly distributed. This makes it a heterogeneous mixture.
Additional Details:
Heterogeneous mixtures like salt and pepper are common in everyday life where components maintain their separate identities and physical properties. They can be separated by simple physical means like picking or sieving. In contrast, homogeneous mixtures (solutions) have components evenly mixed at the molecular level, making them appear as a single substance visually.
Summary:
- Sodium: pure element, not a mixture.
- Baking soda: pure compound, not a mixture.
- Dextrose in water: homogeneous mixture (solution).
- Salt and pepper in a glass: heterogeneous mixture.
Thus, salt and pepper in a glass is the correct answer because it is a mixture with visibly distinct parts.