Density and Laboratory Tech

Experiment (1) Density and Laboratory Tech. Density: mass per unit volume. Density = 𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒 SI unit of mass is Kg, Volume is m3, Density is Kg/m3. 1- Density of solid. DETERMINATION OF UNKNOWN DENSITY Figure a- Mass of solid (g) → from balance. Precision of balance depends on number of decimal points. Example (1): 0. 00⟶𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 𝑖𝑠 ±0. 01. 0. 00⟶𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 𝑖𝑠 ±0. 001. 0. 00⟶𝑃𝑟𝑒𝑐𝑖𝑠𝑖𝑜𝑛 𝑖𝑠 ±0. 0001. Example (2): An object has amass of 6.732g. Precision = + 0.001 b- Volume of water (cm3 – mL) by using graduated cylinder. Precision of cylinder equal to the half of the lowest scaling. Example (3): If the lowest scaling equal to 0.1cm3 precision = 0.1/2 = +0.05. c- immerse the solid completely in water, and observe the increase (displacement) in the volume which is due to volume of solid. Volume of solid = Volume (solid + water) – volume (water). Density of solid = 𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒 (g/cm3). 2- Density of Liquid. a- mass of liquid = (mass of cylinder filled with water) – (mass of empty cylinder). b- density of liquid = = 𝑚𝑎𝑠𝑠 𝑣𝑜𝑙𝑢𝑚𝑒 (g/cm3). Density is intensive property (independent on the amount (mass, volume) of substance. Density is always decrease with increasing of temperature (i.e. the volume increase (expanded)). Example (4): When 4.35g of iron immersed in 3.35ml of water, the volume was increased to 3.89m. Calculate the density of iron. Significant Figures Reference Sheet: For measure number, significant figures relate the certainty of the measurement. As the number of significant figures increases, the more certain the measurement. Rules of Counting: ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant. Example (5): 15 = 2 sig figs Zeros between nonzero digits are ALWAYS significant. (Squished zeros count!) Example (6): 105 = 3 sig figs ALL zeros to the left of the first non-zero (1,2,3,4,5,6,7,8,9) are not significant. Example (7): 0.0005 = 1 sig fig 0.0505 = 3 sig figs If there is a decimal, zero to the right of the last non zero are ALWAYS significant. Example (8): 2.0 = 2 sig figs 0.500 = 3 sig figs General Examples: Nu ber # of Sig Figs Rule(s) 48,923 5 1 3.923 4 1 900.06 5 1,2 0.0004 1 1,3 8.1000 5 1,4 501.040 6 1,2,4 3,000,000 7 1 10.0 3 1,4 0.004050 4 1,2,3,4 ADDING AND SUBTRACTING: Count the number of decimal places. Round to the lowest number of decimal places. Remember, if trying to remove a figure from on answer, round up if 5 or higher. Example (9): 2.5 + 1 = 3.5 which rounds to 4 5.31 – 2.2 = 3.11 which rounds to 3.1 MULTIPLYING AND DIVIDING: Count the number of significant figures. Round to the lowest number of significant. Remember, if trying to remove a figure from an answer, round up if 5 or higher. Example (10): 2.55 * 2 = 5.1 which rounds to 5 10.0 / 3.0 = 3.3333333 which rounds to 3.3 16.5 / 3 = 5.5 which rounds to 6 Accuracy and precision: The more common definition associates accuracy with systematic errors and precision with random errors. Accuracy is how close a measured value is to the actual (true) value. Precision is how close the measured values are to each other. Figure Data and Results: 1- Unknown Irregular Solid Unknown Number: Trail (1) Trail (2) ……………. ……………. ……………. ……………. ± ± ……………. ……………. ……………. ……………. ± ± ……………. ……………. ……………. ……………. ± ± g- Volume of solid ……………. ……………. h- Density of solid ……………. ……………. i- Average Density ……………. ……………. a- Mass of Solid b- Precision c- Volume of water without solid d- Precision e- Volume of water with solid f- Precision 1- Unknown Liquid Unknown Number: Trail (1) Trail (2) a- Mass of flask + stopper ……………. ……………. b- Precision ……………. ……………. ± ± c- Mass of flask + stopper + liquid ……………. ……………. d- Precision ……………. ……………. ± ± e- Mass of liquid ……………. ……………. f- Volume of liquid ……………. ……………. g- Precision ……………. ……………. h- Density of liquid ……………. ……………. i- Average Density ……………. …………….