How many significant figures are there in the following numbers: 10.78, 6.78, 0.78? If these were pH values, to how many significant figures can you express the [H]? Explain any discrepancies between your answers to the two questions.

10.78 → 4 significant figures, pH = 10.78 → [H⁺] = 1.66ₓ10⁻¹¹ M

6.78 → 3 significant figures, pH = 6.78 → [H⁺] = 1.66ₓ10⁻⁷ M

0.78 → 2 significant figures, pH = 0.78 → [H⁺] = 0.166 M

pH always can be expressed by at least 4 significant figures. The [H⁺], can be expressed by, at least 3 significant figures

Explanation:

Significant figures are the numbers of a measurement that have certainty plus a doubtful number (it is associated with the uncertainty in the measurement). For example, if we measure a paper with a ruler and the ruler measures up to centimeters we can say that the paper is 7.5 cm long, with which we know that the paper is 7 cm + 0.5 cm which we associate with uncertainty. In this case we talk about two significant figures. If the sheet measured 7.57 cm we would already be talking about a more precise measurement and in this case with 3 significant figures.

10.78 → 4 significant figures

6.78 → 3 significant figures

0.78 → 2 significant figures

To determine [H⁺], we apply 10^-pH

10⁻¹⁰°⁷⁸ = 1.66ₓ10⁻¹¹ M

10⁻⁶°⁷⁸ = 1.66ₓ10⁻⁷ M

10⁻⁰°⁷⁸ = 0.166 M

plants need sunlight, water, and carbon dioxide to make food. plants use the raw materials of water, nutrients they absorb from soil, and carbon dioxide to make sugars the plant can use. energy from the sun and chlorophyll are also needed.