CHM 1045 Lab Exam 1
Exp 2- If you have the diameter of the cylinder, what is your next step?
Convert diameter to radius
Exp 2- Density Equation
D=m/v
Exp 2- If the same balance that was used in question 4 was used to determine the mass of the metal cylinder, would the calculated value be equal to, higher than, or lower than the true value?
The mass of the metal cylinder would be too high. Since the balance was not zeroed out when you place the cylinder on the balance the mass would be too high.
Exp 2- If the measured volume of the cylinder was lower than the true volume, would the calculated density be higher or lower than the true value?
Higher than the true value (Explanation: d=m/v: if v is too low; d will be too high)
Exp 2- Equation for Mass of Unknown Liquid
Mass of unknown liquid= (mass of beaker + unknown liquid) - (mass of beaker)
Exp 2- Equation for Mass of Water
Mass of water= (mass of beaker + water) - (mass of beaker)
Exp 2- What is cm^3 equal to?
mL
Exp 2- Equation for Radius of cylinder?
r= d/2
Exp 2- Consider a stone column 3.00 ft in diameter and 10.00 ft high. What is its mass in pounds if the density is 3.50 g/mL?
1.) 3.00 ft diameter 2.) convert 3.00 ft to inches to cm---3.00 ft * 12 in/1 ft * 2.54 cm/1 in= 91.4 cm (diameter) 3.) 10.00 ft diameter 4.) convert 10.00 ft to inches to cm---10.00 ft * 12 in/1 ft *2.54 cl/ 1 in= 304.8 cm 5.) V= pi (91.4 cm)^2 * (304.8 cm) -----------------------------= 2.00 x 10^6 cm^3 4 6.) 2.00 x 10^6 mL= 3.50g/1 mL x 1 lb/ 454g = 1.54 x 10^4 lbs
Which of the following list of measurements shows measurements that are accurate, if the actual density is 1.33 g/mL? a. 1.45g/mL, 1.54g/mL, 1.33g/mL, 1.38g/mL b. 1.32g/mL, 1.34g/mL, 1.35g/mL, 1.32g/mL c. 1.49g/mL, 1.51g/mL, 1.50g/mL, 1.50g/mL
b
Which of the following list of measurements shows measurements that are precise? a. 1.45g/mL, 1.54g/mL, 1.33g/mL, 1.38g/mL b. 1.32g/mL, 1.34g/mL, 1.35g/mL, 1.32g/mL c. 1.49g/mL, 1.51g/mL, 1.50g/mL, 1.50g/mL
b and c
Exp 2- What does r, h, and pi stand for?
R= radius H= height pi= 3.142....
Exp 2- What is the density in g/mL of a sphere which weighs 2.00 lb and has a diameter of 7.00 inches?
1.) 2.00 lbs * 454 g/ 1 lb= 908 g 2.) 7.00 in= diameter (7.00 in/2= 3.50 in = radius) 3.) V= 4/3 pi r^3---- 4/3 pi (3.50)^3 4.) convert 3.50 in to cm 5.) 3.50 in * 2.54 cm/ 1 in= 8.89 cm 6.) Vcylinder= 4/3 pi (8.89cm)^3 7.) D=m/v----908g/2.94X 10^3 mL= .309 g/mL
How many uncertain digits should you have in your measured value?
2 uncertain digit
Which of the following instruments would be most accurate to measure 25mL? a. Graduated cylinder b. Beaker c. Flask d. Buret
d
chemical change
A change that occurs when one or more substances change into entirely new substances with different properties.
Accuracy vs. Precision
Accuracy is how close your answer is to the actual value. Precision is how close your answers or results are to each other.
Exp 2- Suppose that a student performed the experiment and the calculations perfectly as directed except that, unknown to the student, the balance was not zeroed but weighed 0.100 g too high throughout the experiment. Would the calculated value for the density of the unknown liquid be correct? That is, would it be equal to, higher than, or lower than the true value.
The calculated value for the density of the unknown would not be correct. The balance needs to be zeroed out prior to each measurement. When you weigh the difference for the volume, the amount would cancel out.
Exp 2- Vcylinder Equation
Vcylinder=pi r^2 h
Exp 2- What is the volume of the cylinder by water displacement formula?
Volume of cylinder= (volume of water in graduated cylinder with unknown) - (volume of original water in graduated cylinder)
Exp 2- Vsphere Equation
Vsphere= 4/3 pi r^3
physical change
a change of matter from one form to another without a change in chemical properties
physical property
a characteristic that can be observed without changing the identity of the substance
chemical property
a property of matter that describes a substance's ability to participate in chemical reactions