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Final Review

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Frederick High School

The document provides information about significant figures and calculations involving heat and changes in temperature. It discusses that measurements contain certain digits and one estimated digit, and defines the rules for determining which digits are significant. It then gives examples of heat calculations using formulas involving heat (q), specific heat (c), change in temperature (ΔT), heat of fusion (Hfus), and heat of vaporization (Hvap).

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Significant Figures a.k.a.- sig figs
Significant Digits The certain digits and one estimated digit of each measurement are significant. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit. 200.5 4 g
Rules for Sig Figs Non zeros are always significant. Zeros between non zeros are significant. Zeros at the end of significant digits following a decimal point are significant. *They show precision in measurement. 4) Place keeper zeros are NOT significant. Zeros preceding significant digits. Zeros following significant digits without a decimal point.
Try These Examples 7.05940 Final zero significant (follows decimal point) 6 significant digits 0.00135 Leading zeros Not significant (place keepers) 3 significant digits 20,400 Final zeros Not significant (place keepers – no decimal) 3 significant digits
Heat Calculations Heat (q) Energy transferred from an object at a higher temperature to an object at a lower temperature. (heat lost = -heat gained) q = mc  T q=mH fus q=mH vap
Heat Calculations A 10.0g sample of iron at 50.4 o C is cooled to 25.0 o C in 50.0g of water. Calculate the amount of heat lost by the iron. c iron= 0.449 J/g o C A 2.1g ice cube at –8.0 o C melts completely and warms to 12.5 o C. How much heat was required? H fus ice = 334 J/g c ice = 2.03 J/g o C c water = 4.18J/g o C
soluble – a substance that dissolves in a solvent insoluble – a substance that does not dissolve in a solvent solvation – the process of surrounding solute particles with solvent particles to form a solution
Solvation When a solid solute is placed in a solvent, the solvent particles completely surround the surface of the solid solute. If attractive forces between the solute particles and the solvent are greater than the attractive forces holding the the solute particles together, the solvent particles pull the solute particles apart and surround them.
+ - - - NaCl Na = Cl = H 2 O H = O = + - + Process of Solvation - + + - + + + - - + + - + - - + - + - + - + - + + - + + - + + - + + - + +
Water- Universal Solvent Polar molecule Dipoles allow solvation of ions and polar molecules
Factors that Affect the Rate of Solvation Agitate the solution (stirring) increase the temperature of solvent increase the surface area of the solute
SOLUBILITY – refers to the maximum amount of solute that will dissolve in a given amount of solvent (at a specified temperature and pressure) saturated – a solution that contains the maximum amount of dissolved solute (for a given temp & pressure than a saturated solution) unsaturated – a solution that contains less dissolved solute (for a given temp & pressure than a saturated solution)
Units of Solubility g of solute 100 g water read these units as: “ grams of solute per 100 grams of water ”
 
Here are some for you to try. What mass of solute will dissolve in 100mL of water at the following temperatures. Also determine which of the three substances is most soluble in water at 15°C. KNO3at 70°C NaCl at 100°C NH4Cl at 90°C  
supersaturated – a solution that contains more dissolved solute than a saturated solution at the same temperature - is above the solubility curve solute will usually precipitate out of solution
Radioactivity There are two main types of radioactivity: Natural and Induced
Natural Radioactivity Occurs in nature Usually large, unstable nuclei Occurs in three ways:  Particle (alpha particle)  Particle (beta particle)  Ray (gamma ray)
Alpha Decay A helium nucleus is released from the nucleus. ( ) The mass decreases by 4 The atomic number decreases by 2 (Because the He nucleus has 2p + and 2n o ) Alpha radiation can be stopped by a piece of paper. Cannot penetrate skin. Not dangerous.
Alpha Decay Example Notice that the uranium has changed into a new element, thorium.
Beta Decay An electron is released from the nucleus when a neutron becomes a proton. The mass is unaffected. (the mass of a neutron is roughly equal to the mass of a proton) The atomic number is increased by 1. Harder to stop and more dangerous.
Beta Decay Example Notice that carbon has changed into nitrogen.
Gamma Decay Pure energy is released from the nucleus. The mass and atomic number are unaffected. Stopped by lead. The most harmful to living tissue.
Gamma Decay Example No new element formed. Gamma radiation (energy) released.
Induced Radioactivity Particles are slammed together to cause transmutation of stable elements. (Nuclear Bombardment) Discovered by Rutherford in 1919.
Uranium-238 Decay Series
Average Atomic Mass (How the number ends up on the periodic table!!) 1 st  Mass of one isotope x % abundance in decimal form (watch SIG FIGS!!) 2 nd  Do this for each isotope of that element 3 rd  Add all individual isotopes together to get the average atomic mass of the element.
1. Calculate the average atomic mass of potassium using the following data: Potassium-39 38.964 amu x 0.9312 = 36.28 amu Potassium-41 40.962 amu x 0.0688 2.82 amu = + Average atomic mass for K = 39.10 amu 6.88 % 40.962 amu Potassium-41 93.12% 38.964 amu Potassium-39 % abundance Mass Isotope
2. Calculate the average atomic mass of magnesium using the following data: Magnesium-24 23.985 amu x 0.7870 = 18.88 amu Magnesium-25 24.986 amu x 0.1013 2.531 amu = + Average atomic mass for K = 24.31 amu + Magnesium-26 25.983 amu x 0.1117 = 2.902 amu 11.17 % 25.983 amu Magnesium-26 10.13 % 24.986 amu Magnesium-25 78.70% 23.985 amu Magnesium-24 % abundance Mass Isotope

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Final Review

  • 2. Significant Digits The certain digits and one estimated digit of each measurement are significant. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit. 200.5 4 g
  • 3. Rules for Sig Figs Non zeros are always significant. Zeros between non zeros are significant. Zeros at the end of significant digits following a decimal point are significant. *They show precision in measurement. 4) Place keeper zeros are NOT significant. Zeros preceding significant digits. Zeros following significant digits without a decimal point.
  • 4. Try These Examples 7.05940 Final zero significant (follows decimal point) 6 significant digits 0.00135 Leading zeros Not significant (place keepers) 3 significant digits 20,400 Final zeros Not significant (place keepers – no decimal) 3 significant digits
  • 5. Heat Calculations Heat (q) Energy transferred from an object at a higher temperature to an object at a lower temperature. (heat lost = -heat gained) q = mc  T q=mH fus q=mH vap
  • 6. Heat Calculations A 10.0g sample of iron at 50.4 o C is cooled to 25.0 o C in 50.0g of water. Calculate the amount of heat lost by the iron. c iron= 0.449 J/g o C A 2.1g ice cube at –8.0 o C melts completely and warms to 12.5 o C. How much heat was required? H fus ice = 334 J/g c ice = 2.03 J/g o C c water = 4.18J/g o C
  • 7. soluble – a substance that dissolves in a solvent insoluble – a substance that does not dissolve in a solvent solvation – the process of surrounding solute particles with solvent particles to form a solution
  • 8. Solvation When a solid solute is placed in a solvent, the solvent particles completely surround the surface of the solid solute. If attractive forces between the solute particles and the solvent are greater than the attractive forces holding the the solute particles together, the solvent particles pull the solute particles apart and surround them.
  • 9. + - - - NaCl Na = Cl = H 2 O H = O = + - + Process of Solvation - + + - + + + - - + + - + - - + - + - + - + - + + - + + - + + - + + - + +
  • 10. Water- Universal Solvent Polar molecule Dipoles allow solvation of ions and polar molecules
  • 11. Factors that Affect the Rate of Solvation Agitate the solution (stirring) increase the temperature of solvent increase the surface area of the solute
  • 12. SOLUBILITY – refers to the maximum amount of solute that will dissolve in a given amount of solvent (at a specified temperature and pressure) saturated – a solution that contains the maximum amount of dissolved solute (for a given temp & pressure than a saturated solution) unsaturated – a solution that contains less dissolved solute (for a given temp & pressure than a saturated solution)
  • 13. Units of Solubility g of solute 100 g water read these units as: “ grams of solute per 100 grams of water ”
  • 14.  
  • 15. Here are some for you to try. What mass of solute will dissolve in 100mL of water at the following temperatures. Also determine which of the three substances is most soluble in water at 15°C. KNO3at 70°C NaCl at 100°C NH4Cl at 90°C  
  • 16. supersaturated – a solution that contains more dissolved solute than a saturated solution at the same temperature - is above the solubility curve solute will usually precipitate out of solution
  • 17. Radioactivity There are two main types of radioactivity: Natural and Induced
  • 18. Natural Radioactivity Occurs in nature Usually large, unstable nuclei Occurs in three ways:  Particle (alpha particle)  Particle (beta particle)  Ray (gamma ray)
  • 19. Alpha Decay A helium nucleus is released from the nucleus. ( ) The mass decreases by 4 The atomic number decreases by 2 (Because the He nucleus has 2p + and 2n o ) Alpha radiation can be stopped by a piece of paper. Cannot penetrate skin. Not dangerous.
  • 20. Alpha Decay Example Notice that the uranium has changed into a new element, thorium.
  • 21. Beta Decay An electron is released from the nucleus when a neutron becomes a proton. The mass is unaffected. (the mass of a neutron is roughly equal to the mass of a proton) The atomic number is increased by 1. Harder to stop and more dangerous.
  • 22. Beta Decay Example Notice that carbon has changed into nitrogen.
  • 23. Gamma Decay Pure energy is released from the nucleus. The mass and atomic number are unaffected. Stopped by lead. The most harmful to living tissue.
  • 24. Gamma Decay Example No new element formed. Gamma radiation (energy) released.
  • 25. Induced Radioactivity Particles are slammed together to cause transmutation of stable elements. (Nuclear Bombardment) Discovered by Rutherford in 1919.
  • 27. Average Atomic Mass (How the number ends up on the periodic table!!) 1 st  Mass of one isotope x % abundance in decimal form (watch SIG FIGS!!) 2 nd  Do this for each isotope of that element 3 rd  Add all individual isotopes together to get the average atomic mass of the element.
  • 28. 1. Calculate the average atomic mass of potassium using the following data: Potassium-39 38.964 amu x 0.9312 = 36.28 amu Potassium-41 40.962 amu x 0.0688 2.82 amu = + Average atomic mass for K = 39.10 amu 6.88 % 40.962 amu Potassium-41 93.12% 38.964 amu Potassium-39 % abundance Mass Isotope
  • 29. 2. Calculate the average atomic mass of magnesium using the following data: Magnesium-24 23.985 amu x 0.7870 = 18.88 amu Magnesium-25 24.986 amu x 0.1013 2.531 amu = + Average atomic mass for K = 24.31 amu + Magnesium-26 25.983 amu x 0.1117 = 2.902 amu 11.17 % 25.983 amu Magnesium-26 10.13 % 24.986 amu Magnesium-25 78.70% 23.985 amu Magnesium-24 % abundance Mass Isotope