Uncertainty in Measurements When recording measurements, you should record all certain digits plus ONE uncertain digit. This means you make an estimate or “guess” for the space between the lines on whatever measuring device you are using. All measurements contain uncertainty.

Identifying a Chemical Reaction Look for: Particles being removed like 1.A gas is formed. (You see bubbles) 2.A precipitate (insoluble solid) is formed. This means a solution will begin to look cloudy. 3.Water is formed. (This can be difficult to determine) One way to tell is through changes in pH levels. Temperature changes Exothermic: Energy is given off. The reaction produces heat or light. Endothermic: Energy is absorbed. The reaction needs the addition of energy (heat or stirring) to continue. Some change in physical properties. (A new substance is formed) There is a color change.

Chemical equations (Reactions): 2 H 2 (g) +O 2 (g)  2 H 2 O (g) +energy Shows how breaking bonds to rearrange atoms to new substances. Reactants The chemicals you start with are “reacted” together Products The chemicals you end up with are “produced” Chemical equations are like sentences that describe how chemicals interact.

Pre-Lab 3: Types of Measurements 1. Qualitative (qualities like color, shape…) - Contains no numbers e.g., The liquid turned blue 2. Quantitative (Amounts) -Contains numbers e.g., The final temperature was 85.0°C

The Thermometer o Determine the temperature by reading the scale on the thermometer at eye level. o Read the temperature by using all certain digits and one uncertain digit. o Certain digits are determined from the calibration marks on the thermometer. o The uncertain digit (the last digit of the reading) is estimated. o On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.

Do not allow the tip to touch the walls or the bottom of the beaker. If the thermometer bulb touches the glass, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the beaker or flask is on a hotplate or in an ice bath.

Reading the Thermometer Determine the readings as shown below on Celsius thermometers: _ _. _  C

Chemical Change A change in which one or more substances are converted into different substances. In fireworks, Heat and light are produced. This is evidence of a chemical change.