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Proper Lab Technique. Measuring a Liquid Volume When a liquid is placed in a piece of laboratory equipment such as a graduated cylinder, buret, or a beaker,

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Presentation on theme: "Proper Lab Technique. Measuring a Liquid Volume When a liquid is placed in a piece of laboratory equipment such as a graduated cylinder, buret, or a beaker,"— Presentation transcript:

1 Proper Lab Technique

2 Measuring a Liquid Volume When a liquid is placed in a piece of laboratory equipment such as a graduated cylinder, buret, or a beaker, you will notice a "curve" at the surface of the liquid. This curve is known as the meniscus.

3 Measuring a Liquid Volume When taking measurement readings it is important to: Read the meniscus at eye level. Do not read the meniscus from above or below eye level. Significant measurement errors may occur Read the bottom of a concave meniscus.

4 Measuring a Liquid Volume The bottom of this meniscus is between 6.0 and 6.1 mL. The correct reading is 6.07 mL

5 Measuring a Liquid Volume The bottom of the meniscus is between 6.6 and 6.7 mL The correct answer is 6.62 mL

6 Measuring a Solid Volume Measuring a Cube or Cuboid A cube is a solid contained by 6 equal squares A cuboid is a solid with 6 rectangular faces; Cube-like. The volume can be determined by multiplying the breadth by the height by the length(bXhXl) therefore, the equation is; V=bhl

7 Measuring a Solid Volume Pyramid Cone Sphere V=(blh)÷3 V=πr 2 h÷3 V=4πr 3 ÷3 r

8 Measuring a Solid Volume When trying to measure the volume of an irregularly shaped object, the "water displacement method" is the most commonly used technique

9 Measuring a Solid Volume Find a graduated cylinder that will be large enough to fit the object being measured. Fill this graduated cylinder enough so that when placed in the graduated cylinder, the object in question will be fully submerged in the water. Also be careful not to put in so much water that the water level will rise past the graduated cylinders markings when the object is placed in the graduated cylinder. After filling the graduated cylinder to a satisfactory level, record the initial volume of the water in your data. Make sure to read the meniscus. Carefully place the object in the graduated cylinder and record the final volume in your data. To calculate the volume of the irregularly shaped object, subtract the initial volume of the water from the final volume of the water and object. V = V f - V i

10 Measuring Temperature The laboratory thermometers are different than thermometers you may be used to using to take your temperature. The liquid in a laboratory thermometer responds quickly to the surroundings, therefore, you should NEVER shake down a laboratory thermometer. When you measure the temperature of a substance, always read the thermometer while it is immersed in the substance. The entire bulb of the thermometer should be immersed in order to get an accurate reading. Do not touch the sides or bottom of the container with the thermometer.

11 Measuring Temperature Common temperature measurements that we encounter everyday are usually given in degrees Fahrenheit (° F). For example, the human body temperature is 98.6 ° F and the weather person reports that wet roads may freeze if the temperature dips below 32 ° F. However, in science, temperature is more commonly reported in degrees Celsius (°C) or Kelvin (K). The following equations are used to convert these temperature scales: Celsius to Fahrenheit: T F = 1.8(T C ) + 32 Fahrenheit to Celsius: T C = (T F - 32)/1.8 Celsius to Kelvin T K = T C

12 Measuring Mass The triple-beam balance measures the mass of an object by balancing the unknown mass with sliding masses of known values. The triple-beam balance is calibrated in grams with a least count of 0.1g. A measurement, then, can be made to 0.01g. Laboratory balances are used to make measurements of an object's mass, not weight. (The weight of an object, as you will learn, is the product of the object's mass, m, and the acceleration due to gravity, g, or W = mg.)

13 Measuring Mass using a triple beam balance 1. Zero the balance before you determine the mass of any substance. a) Slide all of the riders back to the zero point. b) Check to see that the pointer swings freely along the scale. c) Use the adjustment screw to obtain an equal swing of the beams, if necessary. The beam should swing an equal distance above and below the zero point. You must repeat this procedure to "zero" the balance every time you use it.

14 Measuring Mass using a triple beam balance 2. Never put a hot object directly on the balance pan. Any dry chemical that is to be massed should be placed on paper or in a container. Never pour chemicals directly on the balance pan. Remember to mass the paper or container before adding the substance and subtract its mass from the total mass. mass = m f -m i 3. Once you have placed the object to be massed on the pan, move the riders along the beams beginning with the largest mass first. Make sure all riders are in a notch before you take a reading.

15 Measuring Mass using a triple beam balance When balanced, the three beams are added together to determine the total mass of the object; in this example: 200g+ 20g+ 1.50g = g

16 Determining Density Density is the mass per unit volume of a substance under specified conditions of pressure and temperature. To determine the density of an object, you need to find the mass and volume of that object. The units for density will be a unit of mass/unit of volume. Examples: g/mL and kg/cm 3


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