Drupal 7 Adding classes and id for block by preprocess_block From http://drupal.stackexchange.com/questions/30378/how-to-add-id-to-a-block

drupal7-id-class-block-preprocess.php

<?php
  function MODULE_preprocess_block(&$variables) {
    if ($variables['block']->module == 'contact' && $variables['block']->delta == 'contact_block') {
      $variables['block_html_id'] = drupal_html_id('your-id-here');
      $variables['classes_array'][] = drupal_html_class('your-class-here');
    }
  }