| Questions | 5 |
| Topics | Acidity, Base Units, Element, Refraction, Terrestrial Planets |
An acid is a substance that gives up positively charged hydrogen ions (H+) when dissolved in water. A base (alkaline) gives up negatively charged hydroxide ions (OH-) when dissolved in water. pH is a scale that measures of how basic or acidic a solution is. Numbered from 0 to 14, solutions with a pH of 7 are neutral, less than 7 are acidic, more than 7 are alkaline.
| Measurement | Base Unit | Example |
|---|---|---|
| length / distance | meter (m) | km |
| mass | gram (g) | kg |
| volume | liter (L) | mL |
| volume (medical) | cubic centimeter (cc) | cc |
| time | second (s), minute (min), hour (h) | ms, min, h |
| temperature | centigrade (°C) | °C |
An element is matter than cannot be separated into different types of matter by ordinary chemical methods.
Because different materials have different refractive indices, light changes speed when passing from one material to another. This causes the light to bend (refraction) at an angle that depends on the change in refractive index between the materials. The greater the difference, the higher the angle of refraction.
The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) are called terrestrial (Earth-like) planets because, like the Earth, they're solid with inner metal cores covered by rocky surfaces.