Step 1 in the Road to Understanding Chemistry Measurements & Ratios Step 1 in the Road to Understanding Chemistry

Measuring with a Metric Ruler 1 2 3 4 5 cm 6 3.20 3.30 Length of Bar 3.2 cm + estimate between marks = 3.23 cm Special notes: Always start on the zero line, not the end of the ruler Always write down the last used number on the ruler Estimate 1 digit between mm lines (if it is exactly on the line then that next digit is 0)

Sample Measurements Let’s Practice to check your skills cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Length of Bar 10.2 + estimate = 10.26 cm cm 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Length of bar 11.2 cm = 11.20 cm (right on line) Let’s Practice to check your skills

Using Length to Calculate Volume The amount of space an object takes up Volume Units: cm3 (cmcmcm), cubic cm (cc), mL All of the above units are equal May also use any distance unit that is cubed Formulas Prism Volume = Base Area  prism height* For a rectangular prism (box) this means lwh* For a triangular prism this means ½  b  h  h* For a cylinder this means   r2  h* Sphere Volume = 4/3radius3 or 4/3circle arear

Practice Volume of Rectangular Prism (Box) Box Dimensions Calculations Side measurements l = 4 m, w= 2 m, h = 3 m V= lwh V = 4 m  2 m  3 m V = 24 mmm V=24 m3 Side A 3 m 2 m 4 m

Practice Volume of Rectangular Prism (Box) Note: All sides must be in the same unit Box Dimensions Calculations Get sides in same unit (convert all to cm) l = 1 m = 100 cm, w= 30 cm (keep this one), h = 400 mm = 40 cm V= lwh V = 100 cm  30 cm  40 cm V = 120 000 cmcmcm V=120 000 cm3 Side A 400 mm 30 cm 1 m Let’s Practice

Practice Volume of Cylindrical Prism (Box) Note: All measurements must be in the same unit Box Dimensions Calculations r = 10 cm h = 5 cm V= base area · height V =  · r2 · h V = 3.14 · (10 cm)2· 15 cm V= 3.14 · 100 · 15 cm2·cm V = 4710 cm3 10 cm 15 cm Let’s Practice

Practice Volume of Sphere (Ball) Note: Moving to circles Box Dimensions Calculations r = 5 cm V= 4/3 ·  · r3 V = 4/3 · 3.14 · (5 cm)3 V = 4/3 · 3.14· 125 cm3 V = 523.3 cm3 5 cm C = 31.4 cm How would you solve this if all you had was a C = 31.4 cm

Practice Volume of Sphere (Ball) What happens if you can’t measure radius? Box Dimensions Calculations C = 31.4 cm First find r r =C/2 = 31.4 cm/6.28 = 5 cm Plug r into the formula V = 4/3 · 3.14 · (5 cm)3 V = 4/3 · 3.14· 125 cm3 V = 523.3 cm3 5 cm C = 31.4 cm Let’s Practice

Liquid Volume Measuring always use a graduated cylinder to measure liquid volume do NOT use a beaker or flask to accurately measure liquid volume (only approximate ) estimate one decimal place beyond what is marked on the graduated cylinder (like ruler) Watch your scale markings (what is each line worth) Meniscus: curved surface of a liquid in a tube Measure the liquid at the bottom center of the lower curve of the meniscus (bdc) at eye level Note: some plastic cylinders don’t curve the water

Check your skills Measure liquid level here Let’s Practice Activity: Take a graduated cylinder, put some water in it & draw in your notes what the top of the water looks like in the cylinder Measure liquid level here Let’s Practice

Using Liquids to Measure Volume Fill Displacement If the object is hollow you can fill the object with water and measure the amount of liquid What do you do about the side thicknesses? If the object is solid or can’t hold water Fill a container to the brim with water Put object in the water Measure the water that comes out of the container What do you do about floating objects?