CHM110 Principles of Chemistry -1-3.pptx

CHM110 Principles of Chemistry -1-3.pptx

1. A method commonly used to s olve problems involving numbers having units is the unit conversion method or f actor analysis . In this method, a number and its unit is converted to the corresponding new number and unit by means of a conversion factor . Chapter 1 The Language o f Chemistry 1.7 The Use of Units in Calculations: The Unit- Conversio n Method 24 inches = 24 inche s

2. 1.7 The Use of Units in Calculations: The Unit- Conversio n Method Con version factors ar e generally expressed as definitions or equaliti es: 1 mile = 5280 feet From a definition two convers ion factors may be derived: The first factor can b e used to convert feet into miles and the second to convert miles into feet. If a conversion factor is correctly applied, a unit will always cancel .

3. 1.7 The Use of Units in Calculations: The Unit- Conversio n Method Sev eral conver sion steps may be necessary to solve a problem: How many mm are there in 2.5 km? = 2.5 x 10 6 mm How many seconds are there in 7 days? = 6.04800 x 10 5 sec. 6 x 10 5 sec.

4. Length Volume Mass 1 in. = 2.54 c m 1 ft3 = 28.32 L 1 lb = 453.59 g 39.37 in. = 1 m 1.057 qt = 1 L 1 oz = 28.35 g 1 mile = 1.609 km 1 gal = 3.7853 L 1 dram = 1.772 g 1.7 The Use of Units in Calculations: The Unit- Conversio n Method Table 1.5 Rela tions between English and Metric Units

5. 1.7 The Use of Units in Calculations: The Unit- Conversio n Method Example 1.11 Using two or more unit-conversion factors How many milliliters are in 2.35 g allons? 8900 mL 8.90x10 3 mL

6. Mass is a measure of the quantity of matter and is independent of the temperature, pressure, or location of the measurement. The mass of an object is usually measured as i ts weight, however, the weight of an object may change, dependi ng upon location. The weight o f an object at the top of Mt. Everest is about 0.2% less than at sea level. The weight of an objec t in a satellite, orbiting the Earth, is zero. Chapter 1 The Language o f Chemistry 1.8 Two Fundamental Pr operties of Matter: Mass and Volum e

7. 1.8 Two Fundamental Pro perties of Matter: Mass and Volume The mass of an o bject can be accurately measured by comparing its mass to that of a known standard mass by means of a b alance. The SI unit of mass is the k g. This is the only SI base unit that involves a metric prefix.

8. 1.8 Two Fundamental Pro perties of Matter: Mass and Volume The volume of a sample is the amount of space that i t occupies. Devices commonly used to m easure liquid volume: A graduated cylinder has an err or of about 1% ( ± 0.1 mL in 1 mL). Volumetric flasks and pipettes ( fixed volume) and burets (v ariable volume) have an erro r of about 0.1% ( ± 0.01 mL in 10 mL). Hypodermic syringes hav e an error of about 5-6% ( ± 0.5-0.6 mL in 10 mL).

9. 1.8 Two Fundamental Pro perties of Matter: Mass and Volume All volumetric containers are c alibrated in milliliters (mL). One mL is exactly equal to 1 cm 3 . 1000 mL = 1 Li ter = 1000 cm 3 What is 1 Liter in met ers? 1 Liter = 10 −3 m 3 or 10 3 Liter = 1 m 3

10. 1.8 Two Fundamental Pro perties of Matter: Mass and Volume Example 1.13 Converting measures of volume Express a volume of 364 mL in liters.

11. Chapter 1 The Language o f Chemistry 1.9 Density Th e density of an object is the ratio of its mass to its volume : The density of an object varies slightly with temperature because the volume of most substances increases with increasing temperature. Any measurement of density must b e accompanied by value of temperature at which it is measured.

12. 1.9 Density Density is a property of substances in any physical state (solid, liquid or gas ). Can be used to: • evaluate the purity of solids or liq uids • estimate the amount of dissolved solids in solutions • be a conve rsion factor for translating mass into volume or volume into mas s

13. 1.9 Density The density of an object can be used as a factor to convert its mass into its volume and vice-versa: The density of gold is 19.32 g / cm 3 . If we have gold with a volume of 2.000 cm 3 , what is the mass? If we have 38.64 g Au, what is the v olume?

14. The mass of an object is generally measured using a laboratory balance . In the case of a gas or liquid, the sample and its contai ner is weighed and the mass of the empty container is s ubtracted. The volume of a liquid or gas can be obtained from the volume of its containe r. 1.9 Density To measure the density of an object one must first measure i ts mass and its volume. The volume of a regular s olid can be calculated from its dimensions. Alternatively, a nd for an irregular solid, the volu me can be obtained from the volume of liquid displaced when the solid is placed in a partiall y filled graduated cylinder .

15. 1.9 Density An alternative way to measure the density of a liquid is to compare its dens ity to that of a series of objects of known density. • A solid whose densit y is greater than that of the liquid will sink in the liquid. • A solid whose densit y is less than that of the liquid will float on the liquid. • A solid whose dens ity is equal to that of the liquid will remain wherever placed i n the liquid and will neither sink nor float. https://www.teachoo.com/12468/3425/Question-1-Page-6/catego ry/Questions-from-Inside-the-chapter/

16. 1.9 Density A hydrometer is a device based on the above principles that can be used to easily measure the density of a liquid. Most hydrom eters are calibrated to read the ratio of the unknown liquid to that of a reference liquid, usually water. This rati o is known as the specific gravit y of the liquid. A hydrometer is a calibrated floating o bject that rises and falls to a lev el where its density is equal to the density of the liquid in which it is placed. Specific gravity h as no units, since it is the ratio of two densities.

17. Heat will always flow from a hot object to a cold object if t hey are placed in conta ct. The property that is measured to express the “hotness” of an object is called the temperature of the object and is measured using a thermometer . Most common thermometers are based on the fact t hat liquids expand upon heating. If a tube is connected to a reservoir filled with a liquid, the liquid wi ll be forced to rise up in the tube upon heating. Chapter 1 The Lang uage of Chemistry 1.10 Temper ature

18. Celsius scale: Freezing Poi nt marked as Boiling Point marked as 1 00 99 divisions are inscribed Fahrenheit scale: Freezing Point marked as 32 Boiling Poi nt marked as 212 179 division are inscribed 1.10 Tempe rature A thermometer can be calibrated by placing it in freezing water and marking the liquid level, and then placing it in boilin g water and marking the new liquid level .

19. 1.10 Tempe rature Another temperature scale, the Kelvin scale, is almost alw ays used when making scientific t emperature measurements. On this scale, the freezing point of water is 273.15 K and the boiling point of water is 373.15 K. There is a simple relationship betw een the Kelvin scale and the Celsius scale: K = ºC + 273 The relationship between the Fahrenheit and Ce lsius scales is slightly more complicated : or

20. If a temperature is seen to rise 30. degrees on the Celsius scale, how many degrees will it have risen on the Fah renheit scale? 1.10 Tempe rature Example 1.15 Con verting number of Celsius degrees into the equivalent number of Fahren heit degrees